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3084 lines
93 KiB
3084 lines
93 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* mm/page-writeback.c |
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* |
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* Copyright (C) 2002, Linus Torvalds. |
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* Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra |
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* |
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* Contains functions related to writing back dirty pages at the |
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* address_space level. |
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* |
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* 10Apr2002 Andrew Morton |
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* Initial version |
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*/ |
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|
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#include <linux/kernel.h> |
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#include <linux/export.h> |
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#include <linux/spinlock.h> |
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#include <linux/fs.h> |
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#include <linux/mm.h> |
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#include <linux/swap.h> |
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#include <linux/slab.h> |
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#include <linux/pagemap.h> |
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#include <linux/writeback.h> |
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#include <linux/init.h> |
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#include <linux/backing-dev.h> |
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#include <linux/task_io_accounting_ops.h> |
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#include <linux/blkdev.h> |
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#include <linux/mpage.h> |
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#include <linux/rmap.h> |
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#include <linux/percpu.h> |
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#include <linux/smp.h> |
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#include <linux/sysctl.h> |
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#include <linux/cpu.h> |
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#include <linux/syscalls.h> |
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#include <linux/pagevec.h> |
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#include <linux/timer.h> |
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#include <linux/sched/rt.h> |
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#include <linux/sched/signal.h> |
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#include <linux/mm_inline.h> |
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#include <trace/events/writeback.h> |
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|
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#include "internal.h" |
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|
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/* |
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* Sleep at most 200ms at a time in balance_dirty_pages(). |
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*/ |
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#define MAX_PAUSE max(HZ/5, 1) |
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|
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/* |
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* Try to keep balance_dirty_pages() call intervals higher than this many pages |
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* by raising pause time to max_pause when falls below it. |
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*/ |
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#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) |
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|
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/* |
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* Estimate write bandwidth at 200ms intervals. |
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*/ |
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#define BANDWIDTH_INTERVAL max(HZ/5, 1) |
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|
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#define RATELIMIT_CALC_SHIFT 10 |
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|
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/* |
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* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
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* will look to see if it needs to force writeback or throttling. |
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*/ |
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static long ratelimit_pages = 32; |
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|
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/* The following parameters are exported via /proc/sys/vm */ |
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|
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/* |
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* Start background writeback (via writeback threads) at this percentage |
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*/ |
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static int dirty_background_ratio = 10; |
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|
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/* |
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* dirty_background_bytes starts at 0 (disabled) so that it is a function of |
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* dirty_background_ratio * the amount of dirtyable memory |
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*/ |
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static unsigned long dirty_background_bytes; |
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|
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/* |
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* free highmem will not be subtracted from the total free memory |
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* for calculating free ratios if vm_highmem_is_dirtyable is true |
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*/ |
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static int vm_highmem_is_dirtyable; |
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|
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/* |
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* The generator of dirty data starts writeback at this percentage |
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*/ |
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static int vm_dirty_ratio = 20; |
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|
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/* |
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* vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
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* vm_dirty_ratio * the amount of dirtyable memory |
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*/ |
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static unsigned long vm_dirty_bytes; |
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|
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/* |
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* The interval between `kupdate'-style writebacks |
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*/ |
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unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
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EXPORT_SYMBOL_GPL(dirty_writeback_interval); |
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|
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/* |
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* The longest time for which data is allowed to remain dirty |
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*/ |
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unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
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|
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/* |
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* Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
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* a full sync is triggered after this time elapses without any disk activity. |
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*/ |
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int laptop_mode; |
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EXPORT_SYMBOL(laptop_mode); |
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|
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/* End of sysctl-exported parameters */ |
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struct wb_domain global_wb_domain; |
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|
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/* consolidated parameters for balance_dirty_pages() and its subroutines */ |
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struct dirty_throttle_control { |
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#ifdef CONFIG_CGROUP_WRITEBACK |
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struct wb_domain *dom; |
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struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */ |
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#endif |
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struct bdi_writeback *wb; |
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struct fprop_local_percpu *wb_completions; |
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|
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unsigned long avail; /* dirtyable */ |
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unsigned long dirty; /* file_dirty + write + nfs */ |
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unsigned long thresh; /* dirty threshold */ |
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unsigned long bg_thresh; /* dirty background threshold */ |
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|
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unsigned long wb_dirty; /* per-wb counterparts */ |
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unsigned long wb_thresh; |
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unsigned long wb_bg_thresh; |
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|
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unsigned long pos_ratio; |
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}; |
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|
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/* |
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* Length of period for aging writeout fractions of bdis. This is an |
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* arbitrarily chosen number. The longer the period, the slower fractions will |
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* reflect changes in current writeout rate. |
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*/ |
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#define VM_COMPLETIONS_PERIOD_LEN (3*HZ) |
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|
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#ifdef CONFIG_CGROUP_WRITEBACK |
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#define GDTC_INIT(__wb) .wb = (__wb), \ |
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.dom = &global_wb_domain, \ |
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.wb_completions = &(__wb)->completions |
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|
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#define GDTC_INIT_NO_WB .dom = &global_wb_domain |
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|
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#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \ |
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.dom = mem_cgroup_wb_domain(__wb), \ |
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.wb_completions = &(__wb)->memcg_completions, \ |
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.gdtc = __gdtc |
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|
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static bool mdtc_valid(struct dirty_throttle_control *dtc) |
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{ |
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return dtc->dom; |
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} |
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static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) |
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{ |
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return dtc->dom; |
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} |
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static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) |
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{ |
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return mdtc->gdtc; |
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} |
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static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) |
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{ |
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return &wb->memcg_completions; |
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} |
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static void wb_min_max_ratio(struct bdi_writeback *wb, |
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unsigned long *minp, unsigned long *maxp) |
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{ |
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unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth); |
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unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth); |
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unsigned long long min = wb->bdi->min_ratio; |
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unsigned long long max = wb->bdi->max_ratio; |
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|
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/* |
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* @wb may already be clean by the time control reaches here and |
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* the total may not include its bw. |
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*/ |
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if (this_bw < tot_bw) { |
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if (min) { |
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min *= this_bw; |
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min = div64_ul(min, tot_bw); |
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} |
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if (max < 100) { |
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max *= this_bw; |
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max = div64_ul(max, tot_bw); |
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} |
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} |
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*minp = min; |
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*maxp = max; |
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} |
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#else /* CONFIG_CGROUP_WRITEBACK */ |
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|
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#define GDTC_INIT(__wb) .wb = (__wb), \ |
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.wb_completions = &(__wb)->completions |
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#define GDTC_INIT_NO_WB |
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#define MDTC_INIT(__wb, __gdtc) |
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|
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static bool mdtc_valid(struct dirty_throttle_control *dtc) |
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{ |
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return false; |
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} |
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static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) |
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{ |
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return &global_wb_domain; |
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} |
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static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) |
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{ |
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return NULL; |
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} |
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static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) |
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{ |
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return NULL; |
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} |
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static void wb_min_max_ratio(struct bdi_writeback *wb, |
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unsigned long *minp, unsigned long *maxp) |
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{ |
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*minp = wb->bdi->min_ratio; |
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*maxp = wb->bdi->max_ratio; |
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} |
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#endif /* CONFIG_CGROUP_WRITEBACK */ |
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|
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/* |
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* In a memory zone, there is a certain amount of pages we consider |
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* available for the page cache, which is essentially the number of |
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* free and reclaimable pages, minus some zone reserves to protect |
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* lowmem and the ability to uphold the zone's watermarks without |
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* requiring writeback. |
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* |
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* This number of dirtyable pages is the base value of which the |
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* user-configurable dirty ratio is the effective number of pages that |
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* are allowed to be actually dirtied. Per individual zone, or |
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* globally by using the sum of dirtyable pages over all zones. |
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* |
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* Because the user is allowed to specify the dirty limit globally as |
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* absolute number of bytes, calculating the per-zone dirty limit can |
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* require translating the configured limit into a percentage of |
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* global dirtyable memory first. |
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*/ |
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|
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/** |
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* node_dirtyable_memory - number of dirtyable pages in a node |
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* @pgdat: the node |
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* |
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* Return: the node's number of pages potentially available for dirty |
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* page cache. This is the base value for the per-node dirty limits. |
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*/ |
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static unsigned long node_dirtyable_memory(struct pglist_data *pgdat) |
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{ |
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unsigned long nr_pages = 0; |
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int z; |
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for (z = 0; z < MAX_NR_ZONES; z++) { |
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struct zone *zone = pgdat->node_zones + z; |
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if (!populated_zone(zone)) |
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continue; |
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nr_pages += zone_page_state(zone, NR_FREE_PAGES); |
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} |
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/* |
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* Pages reserved for the kernel should not be considered |
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* dirtyable, to prevent a situation where reclaim has to |
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* clean pages in order to balance the zones. |
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*/ |
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nr_pages -= min(nr_pages, pgdat->totalreserve_pages); |
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nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE); |
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nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE); |
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return nr_pages; |
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} |
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static unsigned long highmem_dirtyable_memory(unsigned long total) |
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{ |
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#ifdef CONFIG_HIGHMEM |
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int node; |
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unsigned long x = 0; |
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int i; |
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for_each_node_state(node, N_HIGH_MEMORY) { |
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for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) { |
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struct zone *z; |
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unsigned long nr_pages; |
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if (!is_highmem_idx(i)) |
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continue; |
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z = &NODE_DATA(node)->node_zones[i]; |
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if (!populated_zone(z)) |
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continue; |
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nr_pages = zone_page_state(z, NR_FREE_PAGES); |
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/* watch for underflows */ |
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nr_pages -= min(nr_pages, high_wmark_pages(z)); |
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nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE); |
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nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE); |
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x += nr_pages; |
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} |
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} |
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/* |
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* Make sure that the number of highmem pages is never larger |
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* than the number of the total dirtyable memory. This can only |
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* occur in very strange VM situations but we want to make sure |
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* that this does not occur. |
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*/ |
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return min(x, total); |
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#else |
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return 0; |
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#endif |
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} |
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/** |
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* global_dirtyable_memory - number of globally dirtyable pages |
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* |
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* Return: the global number of pages potentially available for dirty |
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* page cache. This is the base value for the global dirty limits. |
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*/ |
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static unsigned long global_dirtyable_memory(void) |
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{ |
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unsigned long x; |
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x = global_zone_page_state(NR_FREE_PAGES); |
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/* |
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* Pages reserved for the kernel should not be considered |
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* dirtyable, to prevent a situation where reclaim has to |
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* clean pages in order to balance the zones. |
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*/ |
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x -= min(x, totalreserve_pages); |
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x += global_node_page_state(NR_INACTIVE_FILE); |
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x += global_node_page_state(NR_ACTIVE_FILE); |
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if (!vm_highmem_is_dirtyable) |
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x -= highmem_dirtyable_memory(x); |
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return x + 1; /* Ensure that we never return 0 */ |
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} |
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/** |
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* domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain |
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* @dtc: dirty_throttle_control of interest |
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* |
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* Calculate @dtc->thresh and ->bg_thresh considering |
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* vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller |
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* must ensure that @dtc->avail is set before calling this function. The |
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* dirty limits will be lifted by 1/4 for real-time tasks. |
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*/ |
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static void domain_dirty_limits(struct dirty_throttle_control *dtc) |
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{ |
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const unsigned long available_memory = dtc->avail; |
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struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc); |
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unsigned long bytes = vm_dirty_bytes; |
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unsigned long bg_bytes = dirty_background_bytes; |
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/* convert ratios to per-PAGE_SIZE for higher precision */ |
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unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; |
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unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100; |
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unsigned long thresh; |
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unsigned long bg_thresh; |
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struct task_struct *tsk; |
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|
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/* gdtc is !NULL iff @dtc is for memcg domain */ |
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if (gdtc) { |
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unsigned long global_avail = gdtc->avail; |
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|
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/* |
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* The byte settings can't be applied directly to memcg |
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* domains. Convert them to ratios by scaling against |
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* globally available memory. As the ratios are in |
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* per-PAGE_SIZE, they can be obtained by dividing bytes by |
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* number of pages. |
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*/ |
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if (bytes) |
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ratio = min(DIV_ROUND_UP(bytes, global_avail), |
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PAGE_SIZE); |
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if (bg_bytes) |
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bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail), |
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PAGE_SIZE); |
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bytes = bg_bytes = 0; |
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} |
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if (bytes) |
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thresh = DIV_ROUND_UP(bytes, PAGE_SIZE); |
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else |
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thresh = (ratio * available_memory) / PAGE_SIZE; |
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if (bg_bytes) |
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bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE); |
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else |
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bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; |
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if (bg_thresh >= thresh) |
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bg_thresh = thresh / 2; |
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tsk = current; |
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if (rt_task(tsk)) { |
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bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32; |
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thresh += thresh / 4 + global_wb_domain.dirty_limit / 32; |
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} |
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dtc->thresh = thresh; |
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dtc->bg_thresh = bg_thresh; |
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/* we should eventually report the domain in the TP */ |
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if (!gdtc) |
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trace_global_dirty_state(bg_thresh, thresh); |
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} |
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/** |
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* global_dirty_limits - background-writeback and dirty-throttling thresholds |
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* @pbackground: out parameter for bg_thresh |
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* @pdirty: out parameter for thresh |
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* |
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* Calculate bg_thresh and thresh for global_wb_domain. See |
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* domain_dirty_limits() for details. |
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*/ |
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void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) |
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{ |
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struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB }; |
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gdtc.avail = global_dirtyable_memory(); |
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domain_dirty_limits(&gdtc); |
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*pbackground = gdtc.bg_thresh; |
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*pdirty = gdtc.thresh; |
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} |
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/** |
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* node_dirty_limit - maximum number of dirty pages allowed in a node |
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* @pgdat: the node |
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* |
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* Return: the maximum number of dirty pages allowed in a node, based |
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* on the node's dirtyable memory. |
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*/ |
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static unsigned long node_dirty_limit(struct pglist_data *pgdat) |
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{ |
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unsigned long node_memory = node_dirtyable_memory(pgdat); |
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struct task_struct *tsk = current; |
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unsigned long dirty; |
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if (vm_dirty_bytes) |
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dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * |
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node_memory / global_dirtyable_memory(); |
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else |
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dirty = vm_dirty_ratio * node_memory / 100; |
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|
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if (rt_task(tsk)) |
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dirty += dirty / 4; |
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return dirty; |
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} |
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|
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/** |
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* node_dirty_ok - tells whether a node is within its dirty limits |
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* @pgdat: the node to check |
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* |
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* Return: %true when the dirty pages in @pgdat are within the node's |
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* dirty limit, %false if the limit is exceeded. |
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*/ |
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bool node_dirty_ok(struct pglist_data *pgdat) |
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{ |
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unsigned long limit = node_dirty_limit(pgdat); |
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unsigned long nr_pages = 0; |
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|
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nr_pages += node_page_state(pgdat, NR_FILE_DIRTY); |
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nr_pages += node_page_state(pgdat, NR_WRITEBACK); |
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|
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return nr_pages <= limit; |
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} |
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|
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#ifdef CONFIG_SYSCTL |
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static int dirty_background_ratio_handler(struct ctl_table *table, int write, |
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void *buffer, size_t *lenp, loff_t *ppos) |
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{ |
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int ret; |
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|
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ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
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if (ret == 0 && write) |
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dirty_background_bytes = 0; |
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return ret; |
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} |
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|
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static int dirty_background_bytes_handler(struct ctl_table *table, int write, |
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void *buffer, size_t *lenp, loff_t *ppos) |
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{ |
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int ret; |
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|
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ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
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if (ret == 0 && write) |
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dirty_background_ratio = 0; |
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return ret; |
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} |
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|
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static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer, |
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size_t *lenp, loff_t *ppos) |
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{ |
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int old_ratio = vm_dirty_ratio; |
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int ret; |
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|
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ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
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if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
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writeback_set_ratelimit(); |
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vm_dirty_bytes = 0; |
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} |
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return ret; |
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} |
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|
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static int dirty_bytes_handler(struct ctl_table *table, int write, |
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void *buffer, size_t *lenp, loff_t *ppos) |
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{ |
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unsigned long old_bytes = vm_dirty_bytes; |
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int ret; |
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|
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ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
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if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
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writeback_set_ratelimit(); |
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vm_dirty_ratio = 0; |
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} |
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return ret; |
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} |
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#endif |
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|
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static unsigned long wp_next_time(unsigned long cur_time) |
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{ |
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cur_time += VM_COMPLETIONS_PERIOD_LEN; |
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/* 0 has a special meaning... */ |
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if (!cur_time) |
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return 1; |
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return cur_time; |
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} |
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|
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static void wb_domain_writeout_add(struct wb_domain *dom, |
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struct fprop_local_percpu *completions, |
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unsigned int max_prop_frac, long nr) |
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{ |
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__fprop_add_percpu_max(&dom->completions, completions, |
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max_prop_frac, nr); |
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/* First event after period switching was turned off? */ |
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if (unlikely(!dom->period_time)) { |
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/* |
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* We can race with other __bdi_writeout_inc calls here but |
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* it does not cause any harm since the resulting time when |
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* timer will fire and what is in writeout_period_time will be |
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* roughly the same. |
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*/ |
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dom->period_time = wp_next_time(jiffies); |
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mod_timer(&dom->period_timer, dom->period_time); |
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} |
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} |
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|
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/* |
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* Increment @wb's writeout completion count and the global writeout |
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* completion count. Called from __folio_end_writeback(). |
|
*/ |
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static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr) |
|
{ |
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struct wb_domain *cgdom; |
|
|
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wb_stat_mod(wb, WB_WRITTEN, nr); |
|
wb_domain_writeout_add(&global_wb_domain, &wb->completions, |
|
wb->bdi->max_prop_frac, nr); |
|
|
|
cgdom = mem_cgroup_wb_domain(wb); |
|
if (cgdom) |
|
wb_domain_writeout_add(cgdom, wb_memcg_completions(wb), |
|
wb->bdi->max_prop_frac, nr); |
|
} |
|
|
|
void wb_writeout_inc(struct bdi_writeback *wb) |
|
{ |
|
unsigned long flags; |
|
|
|
local_irq_save(flags); |
|
__wb_writeout_add(wb, 1); |
|
local_irq_restore(flags); |
|
} |
|
EXPORT_SYMBOL_GPL(wb_writeout_inc); |
|
|
|
/* |
|
* On idle system, we can be called long after we scheduled because we use |
|
* deferred timers so count with missed periods. |
|
*/ |
|
static void writeout_period(struct timer_list *t) |
|
{ |
|
struct wb_domain *dom = from_timer(dom, t, period_timer); |
|
int miss_periods = (jiffies - dom->period_time) / |
|
VM_COMPLETIONS_PERIOD_LEN; |
|
|
|
if (fprop_new_period(&dom->completions, miss_periods + 1)) { |
|
dom->period_time = wp_next_time(dom->period_time + |
|
miss_periods * VM_COMPLETIONS_PERIOD_LEN); |
|
mod_timer(&dom->period_timer, dom->period_time); |
|
} else { |
|
/* |
|
* Aging has zeroed all fractions. Stop wasting CPU on period |
|
* updates. |
|
*/ |
|
dom->period_time = 0; |
|
} |
|
} |
|
|
|
int wb_domain_init(struct wb_domain *dom, gfp_t gfp) |
|
{ |
|
memset(dom, 0, sizeof(*dom)); |
|
|
|
spin_lock_init(&dom->lock); |
|
|
|
timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE); |
|
|
|
dom->dirty_limit_tstamp = jiffies; |
|
|
|
return fprop_global_init(&dom->completions, gfp); |
|
} |
|
|
|
#ifdef CONFIG_CGROUP_WRITEBACK |
|
void wb_domain_exit(struct wb_domain *dom) |
|
{ |
|
del_timer_sync(&dom->period_timer); |
|
fprop_global_destroy(&dom->completions); |
|
} |
|
#endif |
|
|
|
/* |
|
* bdi_min_ratio keeps the sum of the minimum dirty shares of all |
|
* registered backing devices, which, for obvious reasons, can not |
|
* exceed 100%. |
|
*/ |
|
static unsigned int bdi_min_ratio; |
|
|
|
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
|
{ |
|
unsigned int delta; |
|
int ret = 0; |
|
|
|
spin_lock_bh(&bdi_lock); |
|
if (min_ratio > bdi->max_ratio) { |
|
ret = -EINVAL; |
|
} else { |
|
if (min_ratio < bdi->min_ratio) { |
|
delta = bdi->min_ratio - min_ratio; |
|
bdi_min_ratio -= delta; |
|
bdi->min_ratio = min_ratio; |
|
} else { |
|
delta = min_ratio - bdi->min_ratio; |
|
if (bdi_min_ratio + delta < 100) { |
|
bdi_min_ratio += delta; |
|
bdi->min_ratio = min_ratio; |
|
} else { |
|
ret = -EINVAL; |
|
} |
|
} |
|
} |
|
spin_unlock_bh(&bdi_lock); |
|
|
|
return ret; |
|
} |
|
|
|
int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
|
{ |
|
int ret = 0; |
|
|
|
if (max_ratio > 100) |
|
return -EINVAL; |
|
|
|
spin_lock_bh(&bdi_lock); |
|
if (bdi->min_ratio > max_ratio) { |
|
ret = -EINVAL; |
|
} else { |
|
bdi->max_ratio = max_ratio; |
|
bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; |
|
} |
|
spin_unlock_bh(&bdi_lock); |
|
|
|
return ret; |
|
} |
|
EXPORT_SYMBOL(bdi_set_max_ratio); |
|
|
|
static unsigned long dirty_freerun_ceiling(unsigned long thresh, |
|
unsigned long bg_thresh) |
|
{ |
|
return (thresh + bg_thresh) / 2; |
|
} |
|
|
|
static unsigned long hard_dirty_limit(struct wb_domain *dom, |
|
unsigned long thresh) |
|
{ |
|
return max(thresh, dom->dirty_limit); |
|
} |
|
|
|
/* |
|
* Memory which can be further allocated to a memcg domain is capped by |
|
* system-wide clean memory excluding the amount being used in the domain. |
|
*/ |
|
static void mdtc_calc_avail(struct dirty_throttle_control *mdtc, |
|
unsigned long filepages, unsigned long headroom) |
|
{ |
|
struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc); |
|
unsigned long clean = filepages - min(filepages, mdtc->dirty); |
|
unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty); |
|
unsigned long other_clean = global_clean - min(global_clean, clean); |
|
|
|
mdtc->avail = filepages + min(headroom, other_clean); |
|
} |
|
|
|
/** |
|
* __wb_calc_thresh - @wb's share of dirty throttling threshold |
|
* @dtc: dirty_throttle_context of interest |
|
* |
|
* Note that balance_dirty_pages() will only seriously take it as a hard limit |
|
* when sleeping max_pause per page is not enough to keep the dirty pages under |
|
* control. For example, when the device is completely stalled due to some error |
|
* conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. |
|
* In the other normal situations, it acts more gently by throttling the tasks |
|
* more (rather than completely block them) when the wb dirty pages go high. |
|
* |
|
* It allocates high/low dirty limits to fast/slow devices, in order to prevent |
|
* - starving fast devices |
|
* - piling up dirty pages (that will take long time to sync) on slow devices |
|
* |
|
* The wb's share of dirty limit will be adapting to its throughput and |
|
* bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
|
* |
|
* Return: @wb's dirty limit in pages. The term "dirty" in the context of |
|
* dirty balancing includes all PG_dirty and PG_writeback pages. |
|
*/ |
|
static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc) |
|
{ |
|
struct wb_domain *dom = dtc_dom(dtc); |
|
unsigned long thresh = dtc->thresh; |
|
u64 wb_thresh; |
|
unsigned long numerator, denominator; |
|
unsigned long wb_min_ratio, wb_max_ratio; |
|
|
|
/* |
|
* Calculate this BDI's share of the thresh ratio. |
|
*/ |
|
fprop_fraction_percpu(&dom->completions, dtc->wb_completions, |
|
&numerator, &denominator); |
|
|
|
wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100; |
|
wb_thresh *= numerator; |
|
wb_thresh = div64_ul(wb_thresh, denominator); |
|
|
|
wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); |
|
|
|
wb_thresh += (thresh * wb_min_ratio) / 100; |
|
if (wb_thresh > (thresh * wb_max_ratio) / 100) |
|
wb_thresh = thresh * wb_max_ratio / 100; |
|
|
|
return wb_thresh; |
|
} |
|
|
|
unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh) |
|
{ |
|
struct dirty_throttle_control gdtc = { GDTC_INIT(wb), |
|
.thresh = thresh }; |
|
return __wb_calc_thresh(&gdtc); |
|
} |
|
|
|
/* |
|
* setpoint - dirty 3 |
|
* f(dirty) := 1.0 + (----------------) |
|
* limit - setpoint |
|
* |
|
* it's a 3rd order polynomial that subjects to |
|
* |
|
* (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
|
* (2) f(setpoint) = 1.0 => the balance point |
|
* (3) f(limit) = 0 => the hard limit |
|
* (4) df/dx <= 0 => negative feedback control |
|
* (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
|
* => fast response on large errors; small oscillation near setpoint |
|
*/ |
|
static long long pos_ratio_polynom(unsigned long setpoint, |
|
unsigned long dirty, |
|
unsigned long limit) |
|
{ |
|
long long pos_ratio; |
|
long x; |
|
|
|
x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, |
|
(limit - setpoint) | 1); |
|
pos_ratio = x; |
|
pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
|
pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
|
pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
|
|
|
return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT); |
|
} |
|
|
|
/* |
|
* Dirty position control. |
|
* |
|
* (o) global/bdi setpoints |
|
* |
|
* We want the dirty pages be balanced around the global/wb setpoints. |
|
* When the number of dirty pages is higher/lower than the setpoint, the |
|
* dirty position control ratio (and hence task dirty ratelimit) will be |
|
* decreased/increased to bring the dirty pages back to the setpoint. |
|
* |
|
* pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
|
* |
|
* if (dirty < setpoint) scale up pos_ratio |
|
* if (dirty > setpoint) scale down pos_ratio |
|
* |
|
* if (wb_dirty < wb_setpoint) scale up pos_ratio |
|
* if (wb_dirty > wb_setpoint) scale down pos_ratio |
|
* |
|
* task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
|
* |
|
* (o) global control line |
|
* |
|
* ^ pos_ratio |
|
* | |
|
* | |<===== global dirty control scope ======>| |
|
* 2.0 * * * * * * * |
|
* | .* |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* 1.0 ................................* |
|
* | . . * |
|
* | . . * |
|
* | . . * |
|
* | . . * |
|
* | . . * |
|
* 0 +------------.------------------.----------------------*-------------> |
|
* freerun^ setpoint^ limit^ dirty pages |
|
* |
|
* (o) wb control line |
|
* |
|
* ^ pos_ratio |
|
* | |
|
* | * |
|
* | * |
|
* | * |
|
* | * |
|
* | * |<=========== span ============>| |
|
* 1.0 .......................* |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* | . * |
|
* 1/4 ...............................................* * * * * * * * * * * * |
|
* | . . |
|
* | . . |
|
* | . . |
|
* 0 +----------------------.-------------------------------.-------------> |
|
* wb_setpoint^ x_intercept^ |
|
* |
|
* The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can |
|
* be smoothly throttled down to normal if it starts high in situations like |
|
* - start writing to a slow SD card and a fast disk at the same time. The SD |
|
* card's wb_dirty may rush to many times higher than wb_setpoint. |
|
* - the wb dirty thresh drops quickly due to change of JBOD workload |
|
*/ |
|
static void wb_position_ratio(struct dirty_throttle_control *dtc) |
|
{ |
|
struct bdi_writeback *wb = dtc->wb; |
|
unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth); |
|
unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
|
unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
|
unsigned long wb_thresh = dtc->wb_thresh; |
|
unsigned long x_intercept; |
|
unsigned long setpoint; /* dirty pages' target balance point */ |
|
unsigned long wb_setpoint; |
|
unsigned long span; |
|
long long pos_ratio; /* for scaling up/down the rate limit */ |
|
long x; |
|
|
|
dtc->pos_ratio = 0; |
|
|
|
if (unlikely(dtc->dirty >= limit)) |
|
return; |
|
|
|
/* |
|
* global setpoint |
|
* |
|
* See comment for pos_ratio_polynom(). |
|
*/ |
|
setpoint = (freerun + limit) / 2; |
|
pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit); |
|
|
|
/* |
|
* The strictlimit feature is a tool preventing mistrusted filesystems |
|
* from growing a large number of dirty pages before throttling. For |
|
* such filesystems balance_dirty_pages always checks wb counters |
|
* against wb limits. Even if global "nr_dirty" is under "freerun". |
|
* This is especially important for fuse which sets bdi->max_ratio to |
|
* 1% by default. Without strictlimit feature, fuse writeback may |
|
* consume arbitrary amount of RAM because it is accounted in |
|
* NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". |
|
* |
|
* Here, in wb_position_ratio(), we calculate pos_ratio based on |
|
* two values: wb_dirty and wb_thresh. Let's consider an example: |
|
* total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global |
|
* limits are set by default to 10% and 20% (background and throttle). |
|
* Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. |
|
* wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is |
|
* about ~6K pages (as the average of background and throttle wb |
|
* limits). The 3rd order polynomial will provide positive feedback if |
|
* wb_dirty is under wb_setpoint and vice versa. |
|
* |
|
* Note, that we cannot use global counters in these calculations |
|
* because we want to throttle process writing to a strictlimit wb |
|
* much earlier than global "freerun" is reached (~23MB vs. ~2.3GB |
|
* in the example above). |
|
*/ |
|
if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
|
long long wb_pos_ratio; |
|
|
|
if (dtc->wb_dirty < 8) { |
|
dtc->pos_ratio = min_t(long long, pos_ratio * 2, |
|
2 << RATELIMIT_CALC_SHIFT); |
|
return; |
|
} |
|
|
|
if (dtc->wb_dirty >= wb_thresh) |
|
return; |
|
|
|
wb_setpoint = dirty_freerun_ceiling(wb_thresh, |
|
dtc->wb_bg_thresh); |
|
|
|
if (wb_setpoint == 0 || wb_setpoint == wb_thresh) |
|
return; |
|
|
|
wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty, |
|
wb_thresh); |
|
|
|
/* |
|
* Typically, for strictlimit case, wb_setpoint << setpoint |
|
* and pos_ratio >> wb_pos_ratio. In the other words global |
|
* state ("dirty") is not limiting factor and we have to |
|
* make decision based on wb counters. But there is an |
|
* important case when global pos_ratio should get precedence: |
|
* global limits are exceeded (e.g. due to activities on other |
|
* wb's) while given strictlimit wb is below limit. |
|
* |
|
* "pos_ratio * wb_pos_ratio" would work for the case above, |
|
* but it would look too non-natural for the case of all |
|
* activity in the system coming from a single strictlimit wb |
|
* with bdi->max_ratio == 100%. |
|
* |
|
* Note that min() below somewhat changes the dynamics of the |
|
* control system. Normally, pos_ratio value can be well over 3 |
|
* (when globally we are at freerun and wb is well below wb |
|
* setpoint). Now the maximum pos_ratio in the same situation |
|
* is 2. We might want to tweak this if we observe the control |
|
* system is too slow to adapt. |
|
*/ |
|
dtc->pos_ratio = min(pos_ratio, wb_pos_ratio); |
|
return; |
|
} |
|
|
|
/* |
|
* We have computed basic pos_ratio above based on global situation. If |
|
* the wb is over/under its share of dirty pages, we want to scale |
|
* pos_ratio further down/up. That is done by the following mechanism. |
|
*/ |
|
|
|
/* |
|
* wb setpoint |
|
* |
|
* f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint) |
|
* |
|
* x_intercept - wb_dirty |
|
* := -------------------------- |
|
* x_intercept - wb_setpoint |
|
* |
|
* The main wb control line is a linear function that subjects to |
|
* |
|
* (1) f(wb_setpoint) = 1.0 |
|
* (2) k = - 1 / (8 * write_bw) (in single wb case) |
|
* or equally: x_intercept = wb_setpoint + 8 * write_bw |
|
* |
|
* For single wb case, the dirty pages are observed to fluctuate |
|
* regularly within range |
|
* [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2] |
|
* for various filesystems, where (2) can yield in a reasonable 12.5% |
|
* fluctuation range for pos_ratio. |
|
* |
|
* For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its |
|
* own size, so move the slope over accordingly and choose a slope that |
|
* yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh. |
|
*/ |
|
if (unlikely(wb_thresh > dtc->thresh)) |
|
wb_thresh = dtc->thresh; |
|
/* |
|
* It's very possible that wb_thresh is close to 0 not because the |
|
* device is slow, but that it has remained inactive for long time. |
|
* Honour such devices a reasonable good (hopefully IO efficient) |
|
* threshold, so that the occasional writes won't be blocked and active |
|
* writes can rampup the threshold quickly. |
|
*/ |
|
wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8); |
|
/* |
|
* scale global setpoint to wb's: |
|
* wb_setpoint = setpoint * wb_thresh / thresh |
|
*/ |
|
x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1); |
|
wb_setpoint = setpoint * (u64)x >> 16; |
|
/* |
|
* Use span=(8*write_bw) in single wb case as indicated by |
|
* (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case. |
|
* |
|
* wb_thresh thresh - wb_thresh |
|
* span = --------- * (8 * write_bw) + ------------------ * wb_thresh |
|
* thresh thresh |
|
*/ |
|
span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16; |
|
x_intercept = wb_setpoint + span; |
|
|
|
if (dtc->wb_dirty < x_intercept - span / 4) { |
|
pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty), |
|
(x_intercept - wb_setpoint) | 1); |
|
} else |
|
pos_ratio /= 4; |
|
|
|
/* |
|
* wb reserve area, safeguard against dirty pool underrun and disk idle |
|
* It may push the desired control point of global dirty pages higher |
|
* than setpoint. |
|
*/ |
|
x_intercept = wb_thresh / 2; |
|
if (dtc->wb_dirty < x_intercept) { |
|
if (dtc->wb_dirty > x_intercept / 8) |
|
pos_ratio = div_u64(pos_ratio * x_intercept, |
|
dtc->wb_dirty); |
|
else |
|
pos_ratio *= 8; |
|
} |
|
|
|
dtc->pos_ratio = pos_ratio; |
|
} |
|
|
|
static void wb_update_write_bandwidth(struct bdi_writeback *wb, |
|
unsigned long elapsed, |
|
unsigned long written) |
|
{ |
|
const unsigned long period = roundup_pow_of_two(3 * HZ); |
|
unsigned long avg = wb->avg_write_bandwidth; |
|
unsigned long old = wb->write_bandwidth; |
|
u64 bw; |
|
|
|
/* |
|
* bw = written * HZ / elapsed |
|
* |
|
* bw * elapsed + write_bandwidth * (period - elapsed) |
|
* write_bandwidth = --------------------------------------------------- |
|
* period |
|
* |
|
* @written may have decreased due to folio_account_redirty(). |
|
* Avoid underflowing @bw calculation. |
|
*/ |
|
bw = written - min(written, wb->written_stamp); |
|
bw *= HZ; |
|
if (unlikely(elapsed > period)) { |
|
bw = div64_ul(bw, elapsed); |
|
avg = bw; |
|
goto out; |
|
} |
|
bw += (u64)wb->write_bandwidth * (period - elapsed); |
|
bw >>= ilog2(period); |
|
|
|
/* |
|
* one more level of smoothing, for filtering out sudden spikes |
|
*/ |
|
if (avg > old && old >= (unsigned long)bw) |
|
avg -= (avg - old) >> 3; |
|
|
|
if (avg < old && old <= (unsigned long)bw) |
|
avg += (old - avg) >> 3; |
|
|
|
out: |
|
/* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */ |
|
avg = max(avg, 1LU); |
|
if (wb_has_dirty_io(wb)) { |
|
long delta = avg - wb->avg_write_bandwidth; |
|
WARN_ON_ONCE(atomic_long_add_return(delta, |
|
&wb->bdi->tot_write_bandwidth) <= 0); |
|
} |
|
wb->write_bandwidth = bw; |
|
WRITE_ONCE(wb->avg_write_bandwidth, avg); |
|
} |
|
|
|
static void update_dirty_limit(struct dirty_throttle_control *dtc) |
|
{ |
|
struct wb_domain *dom = dtc_dom(dtc); |
|
unsigned long thresh = dtc->thresh; |
|
unsigned long limit = dom->dirty_limit; |
|
|
|
/* |
|
* Follow up in one step. |
|
*/ |
|
if (limit < thresh) { |
|
limit = thresh; |
|
goto update; |
|
} |
|
|
|
/* |
|
* Follow down slowly. Use the higher one as the target, because thresh |
|
* may drop below dirty. This is exactly the reason to introduce |
|
* dom->dirty_limit which is guaranteed to lie above the dirty pages. |
|
*/ |
|
thresh = max(thresh, dtc->dirty); |
|
if (limit > thresh) { |
|
limit -= (limit - thresh) >> 5; |
|
goto update; |
|
} |
|
return; |
|
update: |
|
dom->dirty_limit = limit; |
|
} |
|
|
|
static void domain_update_dirty_limit(struct dirty_throttle_control *dtc, |
|
unsigned long now) |
|
{ |
|
struct wb_domain *dom = dtc_dom(dtc); |
|
|
|
/* |
|
* check locklessly first to optimize away locking for the most time |
|
*/ |
|
if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) |
|
return; |
|
|
|
spin_lock(&dom->lock); |
|
if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) { |
|
update_dirty_limit(dtc); |
|
dom->dirty_limit_tstamp = now; |
|
} |
|
spin_unlock(&dom->lock); |
|
} |
|
|
|
/* |
|
* Maintain wb->dirty_ratelimit, the base dirty throttle rate. |
|
* |
|
* Normal wb tasks will be curbed at or below it in long term. |
|
* Obviously it should be around (write_bw / N) when there are N dd tasks. |
|
*/ |
|
static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, |
|
unsigned long dirtied, |
|
unsigned long elapsed) |
|
{ |
|
struct bdi_writeback *wb = dtc->wb; |
|
unsigned long dirty = dtc->dirty; |
|
unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
|
unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
|
unsigned long setpoint = (freerun + limit) / 2; |
|
unsigned long write_bw = wb->avg_write_bandwidth; |
|
unsigned long dirty_ratelimit = wb->dirty_ratelimit; |
|
unsigned long dirty_rate; |
|
unsigned long task_ratelimit; |
|
unsigned long balanced_dirty_ratelimit; |
|
unsigned long step; |
|
unsigned long x; |
|
unsigned long shift; |
|
|
|
/* |
|
* The dirty rate will match the writeout rate in long term, except |
|
* when dirty pages are truncated by userspace or re-dirtied by FS. |
|
*/ |
|
dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed; |
|
|
|
/* |
|
* task_ratelimit reflects each dd's dirty rate for the past 200ms. |
|
*/ |
|
task_ratelimit = (u64)dirty_ratelimit * |
|
dtc->pos_ratio >> RATELIMIT_CALC_SHIFT; |
|
task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
|
|
|
/* |
|
* A linear estimation of the "balanced" throttle rate. The theory is, |
|
* if there are N dd tasks, each throttled at task_ratelimit, the wb's |
|
* dirty_rate will be measured to be (N * task_ratelimit). So the below |
|
* formula will yield the balanced rate limit (write_bw / N). |
|
* |
|
* Note that the expanded form is not a pure rate feedback: |
|
* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
|
* but also takes pos_ratio into account: |
|
* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
|
* |
|
* (1) is not realistic because pos_ratio also takes part in balancing |
|
* the dirty rate. Consider the state |
|
* pos_ratio = 0.5 (3) |
|
* rate = 2 * (write_bw / N) (4) |
|
* If (1) is used, it will stuck in that state! Because each dd will |
|
* be throttled at |
|
* task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
|
* yielding |
|
* dirty_rate = N * task_ratelimit = write_bw (6) |
|
* put (6) into (1) we get |
|
* rate_(i+1) = rate_(i) (7) |
|
* |
|
* So we end up using (2) to always keep |
|
* rate_(i+1) ~= (write_bw / N) (8) |
|
* regardless of the value of pos_ratio. As long as (8) is satisfied, |
|
* pos_ratio is able to drive itself to 1.0, which is not only where |
|
* the dirty count meet the setpoint, but also where the slope of |
|
* pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
|
*/ |
|
balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
|
dirty_rate | 1); |
|
/* |
|
* balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw |
|
*/ |
|
if (unlikely(balanced_dirty_ratelimit > write_bw)) |
|
balanced_dirty_ratelimit = write_bw; |
|
|
|
/* |
|
* We could safely do this and return immediately: |
|
* |
|
* wb->dirty_ratelimit = balanced_dirty_ratelimit; |
|
* |
|
* However to get a more stable dirty_ratelimit, the below elaborated |
|
* code makes use of task_ratelimit to filter out singular points and |
|
* limit the step size. |
|
* |
|
* The below code essentially only uses the relative value of |
|
* |
|
* task_ratelimit - dirty_ratelimit |
|
* = (pos_ratio - 1) * dirty_ratelimit |
|
* |
|
* which reflects the direction and size of dirty position error. |
|
*/ |
|
|
|
/* |
|
* dirty_ratelimit will follow balanced_dirty_ratelimit iff |
|
* task_ratelimit is on the same side of dirty_ratelimit, too. |
|
* For example, when |
|
* - dirty_ratelimit > balanced_dirty_ratelimit |
|
* - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
|
* lowering dirty_ratelimit will help meet both the position and rate |
|
* control targets. Otherwise, don't update dirty_ratelimit if it will |
|
* only help meet the rate target. After all, what the users ultimately |
|
* feel and care are stable dirty rate and small position error. |
|
* |
|
* |task_ratelimit - dirty_ratelimit| is used to limit the step size |
|
* and filter out the singular points of balanced_dirty_ratelimit. Which |
|
* keeps jumping around randomly and can even leap far away at times |
|
* due to the small 200ms estimation period of dirty_rate (we want to |
|
* keep that period small to reduce time lags). |
|
*/ |
|
step = 0; |
|
|
|
/* |
|
* For strictlimit case, calculations above were based on wb counters |
|
* and limits (starting from pos_ratio = wb_position_ratio() and up to |
|
* balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). |
|
* Hence, to calculate "step" properly, we have to use wb_dirty as |
|
* "dirty" and wb_setpoint as "setpoint". |
|
* |
|
* We rampup dirty_ratelimit forcibly if wb_dirty is low because |
|
* it's possible that wb_thresh is close to zero due to inactivity |
|
* of backing device. |
|
*/ |
|
if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
|
dirty = dtc->wb_dirty; |
|
if (dtc->wb_dirty < 8) |
|
setpoint = dtc->wb_dirty + 1; |
|
else |
|
setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; |
|
} |
|
|
|
if (dirty < setpoint) { |
|
x = min3(wb->balanced_dirty_ratelimit, |
|
balanced_dirty_ratelimit, task_ratelimit); |
|
if (dirty_ratelimit < x) |
|
step = x - dirty_ratelimit; |
|
} else { |
|
x = max3(wb->balanced_dirty_ratelimit, |
|
balanced_dirty_ratelimit, task_ratelimit); |
|
if (dirty_ratelimit > x) |
|
step = dirty_ratelimit - x; |
|
} |
|
|
|
/* |
|
* Don't pursue 100% rate matching. It's impossible since the balanced |
|
* rate itself is constantly fluctuating. So decrease the track speed |
|
* when it gets close to the target. Helps eliminate pointless tremors. |
|
*/ |
|
shift = dirty_ratelimit / (2 * step + 1); |
|
if (shift < BITS_PER_LONG) |
|
step = DIV_ROUND_UP(step >> shift, 8); |
|
else |
|
step = 0; |
|
|
|
if (dirty_ratelimit < balanced_dirty_ratelimit) |
|
dirty_ratelimit += step; |
|
else |
|
dirty_ratelimit -= step; |
|
|
|
WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL)); |
|
wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
|
|
|
trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit); |
|
} |
|
|
|
static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, |
|
struct dirty_throttle_control *mdtc, |
|
bool update_ratelimit) |
|
{ |
|
struct bdi_writeback *wb = gdtc->wb; |
|
unsigned long now = jiffies; |
|
unsigned long elapsed; |
|
unsigned long dirtied; |
|
unsigned long written; |
|
|
|
spin_lock(&wb->list_lock); |
|
|
|
/* |
|
* Lockless checks for elapsed time are racy and delayed update after |
|
* IO completion doesn't do it at all (to make sure written pages are |
|
* accounted reasonably quickly). Make sure elapsed >= 1 to avoid |
|
* division errors. |
|
*/ |
|
elapsed = max(now - wb->bw_time_stamp, 1UL); |
|
dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]); |
|
written = percpu_counter_read(&wb->stat[WB_WRITTEN]); |
|
|
|
if (update_ratelimit) { |
|
domain_update_dirty_limit(gdtc, now); |
|
wb_update_dirty_ratelimit(gdtc, dirtied, elapsed); |
|
|
|
/* |
|
* @mdtc is always NULL if !CGROUP_WRITEBACK but the |
|
* compiler has no way to figure that out. Help it. |
|
*/ |
|
if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) { |
|
domain_update_dirty_limit(mdtc, now); |
|
wb_update_dirty_ratelimit(mdtc, dirtied, elapsed); |
|
} |
|
} |
|
wb_update_write_bandwidth(wb, elapsed, written); |
|
|
|
wb->dirtied_stamp = dirtied; |
|
wb->written_stamp = written; |
|
WRITE_ONCE(wb->bw_time_stamp, now); |
|
spin_unlock(&wb->list_lock); |
|
} |
|
|
|
void wb_update_bandwidth(struct bdi_writeback *wb) |
|
{ |
|
struct dirty_throttle_control gdtc = { GDTC_INIT(wb) }; |
|
|
|
__wb_update_bandwidth(&gdtc, NULL, false); |
|
} |
|
|
|
/* Interval after which we consider wb idle and don't estimate bandwidth */ |
|
#define WB_BANDWIDTH_IDLE_JIF (HZ) |
|
|
|
static void wb_bandwidth_estimate_start(struct bdi_writeback *wb) |
|
{ |
|
unsigned long now = jiffies; |
|
unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp); |
|
|
|
if (elapsed > WB_BANDWIDTH_IDLE_JIF && |
|
!atomic_read(&wb->writeback_inodes)) { |
|
spin_lock(&wb->list_lock); |
|
wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED); |
|
wb->written_stamp = wb_stat(wb, WB_WRITTEN); |
|
WRITE_ONCE(wb->bw_time_stamp, now); |
|
spin_unlock(&wb->list_lock); |
|
} |
|
} |
|
|
|
/* |
|
* After a task dirtied this many pages, balance_dirty_pages_ratelimited() |
|
* will look to see if it needs to start dirty throttling. |
|
* |
|
* If dirty_poll_interval is too low, big NUMA machines will call the expensive |
|
* global_zone_page_state() too often. So scale it near-sqrt to the safety margin |
|
* (the number of pages we may dirty without exceeding the dirty limits). |
|
*/ |
|
static unsigned long dirty_poll_interval(unsigned long dirty, |
|
unsigned long thresh) |
|
{ |
|
if (thresh > dirty) |
|
return 1UL << (ilog2(thresh - dirty) >> 1); |
|
|
|
return 1; |
|
} |
|
|
|
static unsigned long wb_max_pause(struct bdi_writeback *wb, |
|
unsigned long wb_dirty) |
|
{ |
|
unsigned long bw = READ_ONCE(wb->avg_write_bandwidth); |
|
unsigned long t; |
|
|
|
/* |
|
* Limit pause time for small memory systems. If sleeping for too long |
|
* time, a small pool of dirty/writeback pages may go empty and disk go |
|
* idle. |
|
* |
|
* 8 serves as the safety ratio. |
|
*/ |
|
t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); |
|
t++; |
|
|
|
return min_t(unsigned long, t, MAX_PAUSE); |
|
} |
|
|
|
static long wb_min_pause(struct bdi_writeback *wb, |
|
long max_pause, |
|
unsigned long task_ratelimit, |
|
unsigned long dirty_ratelimit, |
|
int *nr_dirtied_pause) |
|
{ |
|
long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth)); |
|
long lo = ilog2(READ_ONCE(wb->dirty_ratelimit)); |
|
long t; /* target pause */ |
|
long pause; /* estimated next pause */ |
|
int pages; /* target nr_dirtied_pause */ |
|
|
|
/* target for 10ms pause on 1-dd case */ |
|
t = max(1, HZ / 100); |
|
|
|
/* |
|
* Scale up pause time for concurrent dirtiers in order to reduce CPU |
|
* overheads. |
|
* |
|
* (N * 10ms) on 2^N concurrent tasks. |
|
*/ |
|
if (hi > lo) |
|
t += (hi - lo) * (10 * HZ) / 1024; |
|
|
|
/* |
|
* This is a bit convoluted. We try to base the next nr_dirtied_pause |
|
* on the much more stable dirty_ratelimit. However the next pause time |
|
* will be computed based on task_ratelimit and the two rate limits may |
|
* depart considerably at some time. Especially if task_ratelimit goes |
|
* below dirty_ratelimit/2 and the target pause is max_pause, the next |
|
* pause time will be max_pause*2 _trimmed down_ to max_pause. As a |
|
* result task_ratelimit won't be executed faithfully, which could |
|
* eventually bring down dirty_ratelimit. |
|
* |
|
* We apply two rules to fix it up: |
|
* 1) try to estimate the next pause time and if necessary, use a lower |
|
* nr_dirtied_pause so as not to exceed max_pause. When this happens, |
|
* nr_dirtied_pause will be "dancing" with task_ratelimit. |
|
* 2) limit the target pause time to max_pause/2, so that the normal |
|
* small fluctuations of task_ratelimit won't trigger rule (1) and |
|
* nr_dirtied_pause will remain as stable as dirty_ratelimit. |
|
*/ |
|
t = min(t, 1 + max_pause / 2); |
|
pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
|
|
|
/* |
|
* Tiny nr_dirtied_pause is found to hurt I/O performance in the test |
|
* case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. |
|
* When the 16 consecutive reads are often interrupted by some dirty |
|
* throttling pause during the async writes, cfq will go into idles |
|
* (deadline is fine). So push nr_dirtied_pause as high as possible |
|
* until reaches DIRTY_POLL_THRESH=32 pages. |
|
*/ |
|
if (pages < DIRTY_POLL_THRESH) { |
|
t = max_pause; |
|
pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
|
if (pages > DIRTY_POLL_THRESH) { |
|
pages = DIRTY_POLL_THRESH; |
|
t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; |
|
} |
|
} |
|
|
|
pause = HZ * pages / (task_ratelimit + 1); |
|
if (pause > max_pause) { |
|
t = max_pause; |
|
pages = task_ratelimit * t / roundup_pow_of_two(HZ); |
|
} |
|
|
|
*nr_dirtied_pause = pages; |
|
/* |
|
* The minimal pause time will normally be half the target pause time. |
|
*/ |
|
return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; |
|
} |
|
|
|
static inline void wb_dirty_limits(struct dirty_throttle_control *dtc) |
|
{ |
|
struct bdi_writeback *wb = dtc->wb; |
|
unsigned long wb_reclaimable; |
|
|
|
/* |
|
* wb_thresh is not treated as some limiting factor as |
|
* dirty_thresh, due to reasons |
|
* - in JBOD setup, wb_thresh can fluctuate a lot |
|
* - in a system with HDD and USB key, the USB key may somehow |
|
* go into state (wb_dirty >> wb_thresh) either because |
|
* wb_dirty starts high, or because wb_thresh drops low. |
|
* In this case we don't want to hard throttle the USB key |
|
* dirtiers for 100 seconds until wb_dirty drops under |
|
* wb_thresh. Instead the auxiliary wb control line in |
|
* wb_position_ratio() will let the dirtier task progress |
|
* at some rate <= (write_bw / 2) for bringing down wb_dirty. |
|
*/ |
|
dtc->wb_thresh = __wb_calc_thresh(dtc); |
|
dtc->wb_bg_thresh = dtc->thresh ? |
|
div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0; |
|
|
|
/* |
|
* In order to avoid the stacked BDI deadlock we need |
|
* to ensure we accurately count the 'dirty' pages when |
|
* the threshold is low. |
|
* |
|
* Otherwise it would be possible to get thresh+n pages |
|
* reported dirty, even though there are thresh-m pages |
|
* actually dirty; with m+n sitting in the percpu |
|
* deltas. |
|
*/ |
|
if (dtc->wb_thresh < 2 * wb_stat_error()) { |
|
wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); |
|
dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK); |
|
} else { |
|
wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE); |
|
dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK); |
|
} |
|
} |
|
|
|
/* |
|
* balance_dirty_pages() must be called by processes which are generating dirty |
|
* data. It looks at the number of dirty pages in the machine and will force |
|
* the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
|
* If we're over `background_thresh' then the writeback threads are woken to |
|
* perform some writeout. |
|
*/ |
|
static int balance_dirty_pages(struct bdi_writeback *wb, |
|
unsigned long pages_dirtied, unsigned int flags) |
|
{ |
|
struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; |
|
struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; |
|
struct dirty_throttle_control * const gdtc = &gdtc_stor; |
|
struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? |
|
&mdtc_stor : NULL; |
|
struct dirty_throttle_control *sdtc; |
|
unsigned long nr_reclaimable; /* = file_dirty */ |
|
long period; |
|
long pause; |
|
long max_pause; |
|
long min_pause; |
|
int nr_dirtied_pause; |
|
bool dirty_exceeded = false; |
|
unsigned long task_ratelimit; |
|
unsigned long dirty_ratelimit; |
|
struct backing_dev_info *bdi = wb->bdi; |
|
bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; |
|
unsigned long start_time = jiffies; |
|
int ret = 0; |
|
|
|
for (;;) { |
|
unsigned long now = jiffies; |
|
unsigned long dirty, thresh, bg_thresh; |
|
unsigned long m_dirty = 0; /* stop bogus uninit warnings */ |
|
unsigned long m_thresh = 0; |
|
unsigned long m_bg_thresh = 0; |
|
|
|
nr_reclaimable = global_node_page_state(NR_FILE_DIRTY); |
|
gdtc->avail = global_dirtyable_memory(); |
|
gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK); |
|
|
|
domain_dirty_limits(gdtc); |
|
|
|
if (unlikely(strictlimit)) { |
|
wb_dirty_limits(gdtc); |
|
|
|
dirty = gdtc->wb_dirty; |
|
thresh = gdtc->wb_thresh; |
|
bg_thresh = gdtc->wb_bg_thresh; |
|
} else { |
|
dirty = gdtc->dirty; |
|
thresh = gdtc->thresh; |
|
bg_thresh = gdtc->bg_thresh; |
|
} |
|
|
|
if (mdtc) { |
|
unsigned long filepages, headroom, writeback; |
|
|
|
/* |
|
* If @wb belongs to !root memcg, repeat the same |
|
* basic calculations for the memcg domain. |
|
*/ |
|
mem_cgroup_wb_stats(wb, &filepages, &headroom, |
|
&mdtc->dirty, &writeback); |
|
mdtc->dirty += writeback; |
|
mdtc_calc_avail(mdtc, filepages, headroom); |
|
|
|
domain_dirty_limits(mdtc); |
|
|
|
if (unlikely(strictlimit)) { |
|
wb_dirty_limits(mdtc); |
|
m_dirty = mdtc->wb_dirty; |
|
m_thresh = mdtc->wb_thresh; |
|
m_bg_thresh = mdtc->wb_bg_thresh; |
|
} else { |
|
m_dirty = mdtc->dirty; |
|
m_thresh = mdtc->thresh; |
|
m_bg_thresh = mdtc->bg_thresh; |
|
} |
|
} |
|
|
|
/* |
|
* In laptop mode, we wait until hitting the higher threshold |
|
* before starting background writeout, and then write out all |
|
* the way down to the lower threshold. So slow writers cause |
|
* minimal disk activity. |
|
* |
|
* In normal mode, we start background writeout at the lower |
|
* background_thresh, to keep the amount of dirty memory low. |
|
*/ |
|
if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh && |
|
!writeback_in_progress(wb)) |
|
wb_start_background_writeback(wb); |
|
|
|
/* |
|
* Throttle it only when the background writeback cannot |
|
* catch-up. This avoids (excessively) small writeouts |
|
* when the wb limits are ramping up in case of !strictlimit. |
|
* |
|
* In strictlimit case make decision based on the wb counters |
|
* and limits. Small writeouts when the wb limits are ramping |
|
* up are the price we consciously pay for strictlimit-ing. |
|
* |
|
* If memcg domain is in effect, @dirty should be under |
|
* both global and memcg freerun ceilings. |
|
*/ |
|
if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) && |
|
(!mdtc || |
|
m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { |
|
unsigned long intv; |
|
unsigned long m_intv; |
|
|
|
free_running: |
|
intv = dirty_poll_interval(dirty, thresh); |
|
m_intv = ULONG_MAX; |
|
|
|
current->dirty_paused_when = now; |
|
current->nr_dirtied = 0; |
|
if (mdtc) |
|
m_intv = dirty_poll_interval(m_dirty, m_thresh); |
|
current->nr_dirtied_pause = min(intv, m_intv); |
|
break; |
|
} |
|
|
|
/* Start writeback even when in laptop mode */ |
|
if (unlikely(!writeback_in_progress(wb))) |
|
wb_start_background_writeback(wb); |
|
|
|
mem_cgroup_flush_foreign(wb); |
|
|
|
/* |
|
* Calculate global domain's pos_ratio and select the |
|
* global dtc by default. |
|
*/ |
|
if (!strictlimit) { |
|
wb_dirty_limits(gdtc); |
|
|
|
if ((current->flags & PF_LOCAL_THROTTLE) && |
|
gdtc->wb_dirty < |
|
dirty_freerun_ceiling(gdtc->wb_thresh, |
|
gdtc->wb_bg_thresh)) |
|
/* |
|
* LOCAL_THROTTLE tasks must not be throttled |
|
* when below the per-wb freerun ceiling. |
|
*/ |
|
goto free_running; |
|
} |
|
|
|
dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) && |
|
((gdtc->dirty > gdtc->thresh) || strictlimit); |
|
|
|
wb_position_ratio(gdtc); |
|
sdtc = gdtc; |
|
|
|
if (mdtc) { |
|
/* |
|
* If memcg domain is in effect, calculate its |
|
* pos_ratio. @wb should satisfy constraints from |
|
* both global and memcg domains. Choose the one |
|
* w/ lower pos_ratio. |
|
*/ |
|
if (!strictlimit) { |
|
wb_dirty_limits(mdtc); |
|
|
|
if ((current->flags & PF_LOCAL_THROTTLE) && |
|
mdtc->wb_dirty < |
|
dirty_freerun_ceiling(mdtc->wb_thresh, |
|
mdtc->wb_bg_thresh)) |
|
/* |
|
* LOCAL_THROTTLE tasks must not be |
|
* throttled when below the per-wb |
|
* freerun ceiling. |
|
*/ |
|
goto free_running; |
|
} |
|
dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) && |
|
((mdtc->dirty > mdtc->thresh) || strictlimit); |
|
|
|
wb_position_ratio(mdtc); |
|
if (mdtc->pos_ratio < gdtc->pos_ratio) |
|
sdtc = mdtc; |
|
} |
|
|
|
if (dirty_exceeded != wb->dirty_exceeded) |
|
wb->dirty_exceeded = dirty_exceeded; |
|
|
|
if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + |
|
BANDWIDTH_INTERVAL)) |
|
__wb_update_bandwidth(gdtc, mdtc, true); |
|
|
|
/* throttle according to the chosen dtc */ |
|
dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit); |
|
task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >> |
|
RATELIMIT_CALC_SHIFT; |
|
max_pause = wb_max_pause(wb, sdtc->wb_dirty); |
|
min_pause = wb_min_pause(wb, max_pause, |
|
task_ratelimit, dirty_ratelimit, |
|
&nr_dirtied_pause); |
|
|
|
if (unlikely(task_ratelimit == 0)) { |
|
period = max_pause; |
|
pause = max_pause; |
|
goto pause; |
|
} |
|
period = HZ * pages_dirtied / task_ratelimit; |
|
pause = period; |
|
if (current->dirty_paused_when) |
|
pause -= now - current->dirty_paused_when; |
|
/* |
|
* For less than 1s think time (ext3/4 may block the dirtier |
|
* for up to 800ms from time to time on 1-HDD; so does xfs, |
|
* however at much less frequency), try to compensate it in |
|
* future periods by updating the virtual time; otherwise just |
|
* do a reset, as it may be a light dirtier. |
|
*/ |
|
if (pause < min_pause) { |
|
trace_balance_dirty_pages(wb, |
|
sdtc->thresh, |
|
sdtc->bg_thresh, |
|
sdtc->dirty, |
|
sdtc->wb_thresh, |
|
sdtc->wb_dirty, |
|
dirty_ratelimit, |
|
task_ratelimit, |
|
pages_dirtied, |
|
period, |
|
min(pause, 0L), |
|
start_time); |
|
if (pause < -HZ) { |
|
current->dirty_paused_when = now; |
|
current->nr_dirtied = 0; |
|
} else if (period) { |
|
current->dirty_paused_when += period; |
|
current->nr_dirtied = 0; |
|
} else if (current->nr_dirtied_pause <= pages_dirtied) |
|
current->nr_dirtied_pause += pages_dirtied; |
|
break; |
|
} |
|
if (unlikely(pause > max_pause)) { |
|
/* for occasional dropped task_ratelimit */ |
|
now += min(pause - max_pause, max_pause); |
|
pause = max_pause; |
|
} |
|
|
|
pause: |
|
trace_balance_dirty_pages(wb, |
|
sdtc->thresh, |
|
sdtc->bg_thresh, |
|
sdtc->dirty, |
|
sdtc->wb_thresh, |
|
sdtc->wb_dirty, |
|
dirty_ratelimit, |
|
task_ratelimit, |
|
pages_dirtied, |
|
period, |
|
pause, |
|
start_time); |
|
if (flags & BDP_ASYNC) { |
|
ret = -EAGAIN; |
|
break; |
|
} |
|
__set_current_state(TASK_KILLABLE); |
|
wb->dirty_sleep = now; |
|
io_schedule_timeout(pause); |
|
|
|
current->dirty_paused_when = now + pause; |
|
current->nr_dirtied = 0; |
|
current->nr_dirtied_pause = nr_dirtied_pause; |
|
|
|
/* |
|
* This is typically equal to (dirty < thresh) and can also |
|
* keep "1000+ dd on a slow USB stick" under control. |
|
*/ |
|
if (task_ratelimit) |
|
break; |
|
|
|
/* |
|
* In the case of an unresponsive NFS server and the NFS dirty |
|
* pages exceeds dirty_thresh, give the other good wb's a pipe |
|
* to go through, so that tasks on them still remain responsive. |
|
* |
|
* In theory 1 page is enough to keep the consumer-producer |
|
* pipe going: the flusher cleans 1 page => the task dirties 1 |
|
* more page. However wb_dirty has accounting errors. So use |
|
* the larger and more IO friendly wb_stat_error. |
|
*/ |
|
if (sdtc->wb_dirty <= wb_stat_error()) |
|
break; |
|
|
|
if (fatal_signal_pending(current)) |
|
break; |
|
} |
|
return ret; |
|
} |
|
|
|
static DEFINE_PER_CPU(int, bdp_ratelimits); |
|
|
|
/* |
|
* Normal tasks are throttled by |
|
* loop { |
|
* dirty tsk->nr_dirtied_pause pages; |
|
* take a snap in balance_dirty_pages(); |
|
* } |
|
* However there is a worst case. If every task exit immediately when dirtied |
|
* (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be |
|
* called to throttle the page dirties. The solution is to save the not yet |
|
* throttled page dirties in dirty_throttle_leaks on task exit and charge them |
|
* randomly into the running tasks. This works well for the above worst case, |
|
* as the new task will pick up and accumulate the old task's leaked dirty |
|
* count and eventually get throttled. |
|
*/ |
|
DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; |
|
|
|
/** |
|
* balance_dirty_pages_ratelimited_flags - Balance dirty memory state. |
|
* @mapping: address_space which was dirtied. |
|
* @flags: BDP flags. |
|
* |
|
* Processes which are dirtying memory should call in here once for each page |
|
* which was newly dirtied. The function will periodically check the system's |
|
* dirty state and will initiate writeback if needed. |
|
* |
|
* See balance_dirty_pages_ratelimited() for details. |
|
* |
|
* Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to |
|
* indicate that memory is out of balance and the caller must wait |
|
* for I/O to complete. Otherwise, it will return 0 to indicate |
|
* that either memory was already in balance, or it was able to sleep |
|
* until the amount of dirty memory returned to balance. |
|
*/ |
|
int balance_dirty_pages_ratelimited_flags(struct address_space *mapping, |
|
unsigned int flags) |
|
{ |
|
struct inode *inode = mapping->host; |
|
struct backing_dev_info *bdi = inode_to_bdi(inode); |
|
struct bdi_writeback *wb = NULL; |
|
int ratelimit; |
|
int ret = 0; |
|
int *p; |
|
|
|
if (!(bdi->capabilities & BDI_CAP_WRITEBACK)) |
|
return ret; |
|
|
|
if (inode_cgwb_enabled(inode)) |
|
wb = wb_get_create_current(bdi, GFP_KERNEL); |
|
if (!wb) |
|
wb = &bdi->wb; |
|
|
|
ratelimit = current->nr_dirtied_pause; |
|
if (wb->dirty_exceeded) |
|
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
|
|
|
preempt_disable(); |
|
/* |
|
* This prevents one CPU to accumulate too many dirtied pages without |
|
* calling into balance_dirty_pages(), which can happen when there are |
|
* 1000+ tasks, all of them start dirtying pages at exactly the same |
|
* time, hence all honoured too large initial task->nr_dirtied_pause. |
|
*/ |
|
p = this_cpu_ptr(&bdp_ratelimits); |
|
if (unlikely(current->nr_dirtied >= ratelimit)) |
|
*p = 0; |
|
else if (unlikely(*p >= ratelimit_pages)) { |
|
*p = 0; |
|
ratelimit = 0; |
|
} |
|
/* |
|
* Pick up the dirtied pages by the exited tasks. This avoids lots of |
|
* short-lived tasks (eg. gcc invocations in a kernel build) escaping |
|
* the dirty throttling and livelock other long-run dirtiers. |
|
*/ |
|
p = this_cpu_ptr(&dirty_throttle_leaks); |
|
if (*p > 0 && current->nr_dirtied < ratelimit) { |
|
unsigned long nr_pages_dirtied; |
|
nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); |
|
*p -= nr_pages_dirtied; |
|
current->nr_dirtied += nr_pages_dirtied; |
|
} |
|
preempt_enable(); |
|
|
|
if (unlikely(current->nr_dirtied >= ratelimit)) |
|
ret = balance_dirty_pages(wb, current->nr_dirtied, flags); |
|
|
|
wb_put(wb); |
|
return ret; |
|
} |
|
EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags); |
|
|
|
/** |
|
* balance_dirty_pages_ratelimited - balance dirty memory state. |
|
* @mapping: address_space which was dirtied. |
|
* |
|
* Processes which are dirtying memory should call in here once for each page |
|
* which was newly dirtied. The function will periodically check the system's |
|
* dirty state and will initiate writeback if needed. |
|
* |
|
* Once we're over the dirty memory limit we decrease the ratelimiting |
|
* by a lot, to prevent individual processes from overshooting the limit |
|
* by (ratelimit_pages) each. |
|
*/ |
|
void balance_dirty_pages_ratelimited(struct address_space *mapping) |
|
{ |
|
balance_dirty_pages_ratelimited_flags(mapping, 0); |
|
} |
|
EXPORT_SYMBOL(balance_dirty_pages_ratelimited); |
|
|
|
/** |
|
* wb_over_bg_thresh - does @wb need to be written back? |
|
* @wb: bdi_writeback of interest |
|
* |
|
* Determines whether background writeback should keep writing @wb or it's |
|
* clean enough. |
|
* |
|
* Return: %true if writeback should continue. |
|
*/ |
|
bool wb_over_bg_thresh(struct bdi_writeback *wb) |
|
{ |
|
struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; |
|
struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; |
|
struct dirty_throttle_control * const gdtc = &gdtc_stor; |
|
struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? |
|
&mdtc_stor : NULL; |
|
unsigned long reclaimable; |
|
unsigned long thresh; |
|
|
|
/* |
|
* Similar to balance_dirty_pages() but ignores pages being written |
|
* as we're trying to decide whether to put more under writeback. |
|
*/ |
|
gdtc->avail = global_dirtyable_memory(); |
|
gdtc->dirty = global_node_page_state(NR_FILE_DIRTY); |
|
domain_dirty_limits(gdtc); |
|
|
|
if (gdtc->dirty > gdtc->bg_thresh) |
|
return true; |
|
|
|
thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh); |
|
if (thresh < 2 * wb_stat_error()) |
|
reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); |
|
else |
|
reclaimable = wb_stat(wb, WB_RECLAIMABLE); |
|
|
|
if (reclaimable > thresh) |
|
return true; |
|
|
|
if (mdtc) { |
|
unsigned long filepages, headroom, writeback; |
|
|
|
mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty, |
|
&writeback); |
|
mdtc_calc_avail(mdtc, filepages, headroom); |
|
domain_dirty_limits(mdtc); /* ditto, ignore writeback */ |
|
|
|
if (mdtc->dirty > mdtc->bg_thresh) |
|
return true; |
|
|
|
thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh); |
|
if (thresh < 2 * wb_stat_error()) |
|
reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); |
|
else |
|
reclaimable = wb_stat(wb, WB_RECLAIMABLE); |
|
|
|
if (reclaimable > thresh) |
|
return true; |
|
} |
|
|
|
return false; |
|
} |
|
|
|
#ifdef CONFIG_SYSCTL |
|
/* |
|
* sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
|
*/ |
|
static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write, |
|
void *buffer, size_t *length, loff_t *ppos) |
|
{ |
|
unsigned int old_interval = dirty_writeback_interval; |
|
int ret; |
|
|
|
ret = proc_dointvec(table, write, buffer, length, ppos); |
|
|
|
/* |
|
* Writing 0 to dirty_writeback_interval will disable periodic writeback |
|
* and a different non-zero value will wakeup the writeback threads. |
|
* wb_wakeup_delayed() would be more appropriate, but it's a pain to |
|
* iterate over all bdis and wbs. |
|
* The reason we do this is to make the change take effect immediately. |
|
*/ |
|
if (!ret && write && dirty_writeback_interval && |
|
dirty_writeback_interval != old_interval) |
|
wakeup_flusher_threads(WB_REASON_PERIODIC); |
|
|
|
return ret; |
|
} |
|
#endif |
|
|
|
void laptop_mode_timer_fn(struct timer_list *t) |
|
{ |
|
struct backing_dev_info *backing_dev_info = |
|
from_timer(backing_dev_info, t, laptop_mode_wb_timer); |
|
|
|
wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER); |
|
} |
|
|
|
/* |
|
* We've spun up the disk and we're in laptop mode: schedule writeback |
|
* of all dirty data a few seconds from now. If the flush is already scheduled |
|
* then push it back - the user is still using the disk. |
|
*/ |
|
void laptop_io_completion(struct backing_dev_info *info) |
|
{ |
|
mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
|
} |
|
|
|
/* |
|
* We're in laptop mode and we've just synced. The sync's writes will have |
|
* caused another writeback to be scheduled by laptop_io_completion. |
|
* Nothing needs to be written back anymore, so we unschedule the writeback. |
|
*/ |
|
void laptop_sync_completion(void) |
|
{ |
|
struct backing_dev_info *bdi; |
|
|
|
rcu_read_lock(); |
|
|
|
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
|
del_timer(&bdi->laptop_mode_wb_timer); |
|
|
|
rcu_read_unlock(); |
|
} |
|
|
|
/* |
|
* If ratelimit_pages is too high then we can get into dirty-data overload |
|
* if a large number of processes all perform writes at the same time. |
|
* |
|
* Here we set ratelimit_pages to a level which ensures that when all CPUs are |
|
* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
|
* thresholds. |
|
*/ |
|
|
|
void writeback_set_ratelimit(void) |
|
{ |
|
struct wb_domain *dom = &global_wb_domain; |
|
unsigned long background_thresh; |
|
unsigned long dirty_thresh; |
|
|
|
global_dirty_limits(&background_thresh, &dirty_thresh); |
|
dom->dirty_limit = dirty_thresh; |
|
ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
|
if (ratelimit_pages < 16) |
|
ratelimit_pages = 16; |
|
} |
|
|
|
static int page_writeback_cpu_online(unsigned int cpu) |
|
{ |
|
writeback_set_ratelimit(); |
|
return 0; |
|
} |
|
|
|
#ifdef CONFIG_SYSCTL |
|
|
|
/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */ |
|
static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE; |
|
|
|
static struct ctl_table vm_page_writeback_sysctls[] = { |
|
{ |
|
.procname = "dirty_background_ratio", |
|
.data = &dirty_background_ratio, |
|
.maxlen = sizeof(dirty_background_ratio), |
|
.mode = 0644, |
|
.proc_handler = dirty_background_ratio_handler, |
|
.extra1 = SYSCTL_ZERO, |
|
.extra2 = SYSCTL_ONE_HUNDRED, |
|
}, |
|
{ |
|
.procname = "dirty_background_bytes", |
|
.data = &dirty_background_bytes, |
|
.maxlen = sizeof(dirty_background_bytes), |
|
.mode = 0644, |
|
.proc_handler = dirty_background_bytes_handler, |
|
.extra1 = SYSCTL_LONG_ONE, |
|
}, |
|
{ |
|
.procname = "dirty_ratio", |
|
.data = &vm_dirty_ratio, |
|
.maxlen = sizeof(vm_dirty_ratio), |
|
.mode = 0644, |
|
.proc_handler = dirty_ratio_handler, |
|
.extra1 = SYSCTL_ZERO, |
|
.extra2 = SYSCTL_ONE_HUNDRED, |
|
}, |
|
{ |
|
.procname = "dirty_bytes", |
|
.data = &vm_dirty_bytes, |
|
.maxlen = sizeof(vm_dirty_bytes), |
|
.mode = 0644, |
|
.proc_handler = dirty_bytes_handler, |
|
.extra1 = (void *)&dirty_bytes_min, |
|
}, |
|
{ |
|
.procname = "dirty_writeback_centisecs", |
|
.data = &dirty_writeback_interval, |
|
.maxlen = sizeof(dirty_writeback_interval), |
|
.mode = 0644, |
|
.proc_handler = dirty_writeback_centisecs_handler, |
|
}, |
|
{ |
|
.procname = "dirty_expire_centisecs", |
|
.data = &dirty_expire_interval, |
|
.maxlen = sizeof(dirty_expire_interval), |
|
.mode = 0644, |
|
.proc_handler = proc_dointvec_minmax, |
|
.extra1 = SYSCTL_ZERO, |
|
}, |
|
#ifdef CONFIG_HIGHMEM |
|
{ |
|
.procname = "highmem_is_dirtyable", |
|
.data = &vm_highmem_is_dirtyable, |
|
.maxlen = sizeof(vm_highmem_is_dirtyable), |
|
.mode = 0644, |
|
.proc_handler = proc_dointvec_minmax, |
|
.extra1 = SYSCTL_ZERO, |
|
.extra2 = SYSCTL_ONE, |
|
}, |
|
#endif |
|
{ |
|
.procname = "laptop_mode", |
|
.data = &laptop_mode, |
|
.maxlen = sizeof(laptop_mode), |
|
.mode = 0644, |
|
.proc_handler = proc_dointvec_jiffies, |
|
}, |
|
{} |
|
}; |
|
#endif |
|
|
|
/* |
|
* Called early on to tune the page writeback dirty limits. |
|
* |
|
* We used to scale dirty pages according to how total memory |
|
* related to pages that could be allocated for buffers. |
|
* |
|
* However, that was when we used "dirty_ratio" to scale with |
|
* all memory, and we don't do that any more. "dirty_ratio" |
|
* is now applied to total non-HIGHPAGE memory, and as such we can't |
|
* get into the old insane situation any more where we had |
|
* large amounts of dirty pages compared to a small amount of |
|
* non-HIGHMEM memory. |
|
* |
|
* But we might still want to scale the dirty_ratio by how |
|
* much memory the box has.. |
|
*/ |
|
void __init page_writeback_init(void) |
|
{ |
|
BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL)); |
|
|
|
cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online", |
|
page_writeback_cpu_online, NULL); |
|
cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL, |
|
page_writeback_cpu_online); |
|
#ifdef CONFIG_SYSCTL |
|
register_sysctl_init("vm", vm_page_writeback_sysctls); |
|
#endif |
|
} |
|
|
|
/** |
|
* tag_pages_for_writeback - tag pages to be written by write_cache_pages |
|
* @mapping: address space structure to write |
|
* @start: starting page index |
|
* @end: ending page index (inclusive) |
|
* |
|
* This function scans the page range from @start to @end (inclusive) and tags |
|
* all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
|
* that write_cache_pages (or whoever calls this function) will then use |
|
* TOWRITE tag to identify pages eligible for writeback. This mechanism is |
|
* used to avoid livelocking of writeback by a process steadily creating new |
|
* dirty pages in the file (thus it is important for this function to be quick |
|
* so that it can tag pages faster than a dirtying process can create them). |
|
*/ |
|
void tag_pages_for_writeback(struct address_space *mapping, |
|
pgoff_t start, pgoff_t end) |
|
{ |
|
XA_STATE(xas, &mapping->i_pages, start); |
|
unsigned int tagged = 0; |
|
void *page; |
|
|
|
xas_lock_irq(&xas); |
|
xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) { |
|
xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE); |
|
if (++tagged % XA_CHECK_SCHED) |
|
continue; |
|
|
|
xas_pause(&xas); |
|
xas_unlock_irq(&xas); |
|
cond_resched(); |
|
xas_lock_irq(&xas); |
|
} |
|
xas_unlock_irq(&xas); |
|
} |
|
EXPORT_SYMBOL(tag_pages_for_writeback); |
|
|
|
/** |
|
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
|
* @mapping: address space structure to write |
|
* @wbc: subtract the number of written pages from *@wbc->nr_to_write |
|
* @writepage: function called for each page |
|
* @data: data passed to writepage function |
|
* |
|
* If a page is already under I/O, write_cache_pages() skips it, even |
|
* if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
|
* but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
|
* and msync() need to guarantee that all the data which was dirty at the time |
|
* the call was made get new I/O started against them. If wbc->sync_mode is |
|
* WB_SYNC_ALL then we were called for data integrity and we must wait for |
|
* existing IO to complete. |
|
* |
|
* To avoid livelocks (when other process dirties new pages), we first tag |
|
* pages which should be written back with TOWRITE tag and only then start |
|
* writing them. For data-integrity sync we have to be careful so that we do |
|
* not miss some pages (e.g., because some other process has cleared TOWRITE |
|
* tag we set). The rule we follow is that TOWRITE tag can be cleared only |
|
* by the process clearing the DIRTY tag (and submitting the page for IO). |
|
* |
|
* To avoid deadlocks between range_cyclic writeback and callers that hold |
|
* pages in PageWriteback to aggregate IO until write_cache_pages() returns, |
|
* we do not loop back to the start of the file. Doing so causes a page |
|
* lock/page writeback access order inversion - we should only ever lock |
|
* multiple pages in ascending page->index order, and looping back to the start |
|
* of the file violates that rule and causes deadlocks. |
|
* |
|
* Return: %0 on success, negative error code otherwise |
|
*/ |
|
int write_cache_pages(struct address_space *mapping, |
|
struct writeback_control *wbc, writepage_t writepage, |
|
void *data) |
|
{ |
|
int ret = 0; |
|
int done = 0; |
|
int error; |
|
struct pagevec pvec; |
|
int nr_pages; |
|
pgoff_t index; |
|
pgoff_t end; /* Inclusive */ |
|
pgoff_t done_index; |
|
int range_whole = 0; |
|
xa_mark_t tag; |
|
|
|
pagevec_init(&pvec); |
|
if (wbc->range_cyclic) { |
|
index = mapping->writeback_index; /* prev offset */ |
|
end = -1; |
|
} else { |
|
index = wbc->range_start >> PAGE_SHIFT; |
|
end = wbc->range_end >> PAGE_SHIFT; |
|
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
|
range_whole = 1; |
|
} |
|
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) { |
|
tag_pages_for_writeback(mapping, index, end); |
|
tag = PAGECACHE_TAG_TOWRITE; |
|
} else { |
|
tag = PAGECACHE_TAG_DIRTY; |
|
} |
|
done_index = index; |
|
while (!done && (index <= end)) { |
|
int i; |
|
|
|
nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end, |
|
tag); |
|
if (nr_pages == 0) |
|
break; |
|
|
|
for (i = 0; i < nr_pages; i++) { |
|
struct page *page = pvec.pages[i]; |
|
|
|
done_index = page->index; |
|
|
|
lock_page(page); |
|
|
|
/* |
|
* Page truncated or invalidated. We can freely skip it |
|
* then, even for data integrity operations: the page |
|
* has disappeared concurrently, so there could be no |
|
* real expectation of this data integrity operation |
|
* even if there is now a new, dirty page at the same |
|
* pagecache address. |
|
*/ |
|
if (unlikely(page->mapping != mapping)) { |
|
continue_unlock: |
|
unlock_page(page); |
|
continue; |
|
} |
|
|
|
if (!PageDirty(page)) { |
|
/* someone wrote it for us */ |
|
goto continue_unlock; |
|
} |
|
|
|
if (PageWriteback(page)) { |
|
if (wbc->sync_mode != WB_SYNC_NONE) |
|
wait_on_page_writeback(page); |
|
else |
|
goto continue_unlock; |
|
} |
|
|
|
BUG_ON(PageWriteback(page)); |
|
if (!clear_page_dirty_for_io(page)) |
|
goto continue_unlock; |
|
|
|
trace_wbc_writepage(wbc, inode_to_bdi(mapping->host)); |
|
error = (*writepage)(page, wbc, data); |
|
if (unlikely(error)) { |
|
/* |
|
* Handle errors according to the type of |
|
* writeback. There's no need to continue for |
|
* background writeback. Just push done_index |
|
* past this page so media errors won't choke |
|
* writeout for the entire file. For integrity |
|
* writeback, we must process the entire dirty |
|
* set regardless of errors because the fs may |
|
* still have state to clear for each page. In |
|
* that case we continue processing and return |
|
* the first error. |
|
*/ |
|
if (error == AOP_WRITEPAGE_ACTIVATE) { |
|
unlock_page(page); |
|
error = 0; |
|
} else if (wbc->sync_mode != WB_SYNC_ALL) { |
|
ret = error; |
|
done_index = page->index + 1; |
|
done = 1; |
|
break; |
|
} |
|
if (!ret) |
|
ret = error; |
|
} |
|
|
|
/* |
|
* We stop writing back only if we are not doing |
|
* integrity sync. In case of integrity sync we have to |
|
* keep going until we have written all the pages |
|
* we tagged for writeback prior to entering this loop. |
|
*/ |
|
if (--wbc->nr_to_write <= 0 && |
|
wbc->sync_mode == WB_SYNC_NONE) { |
|
done = 1; |
|
break; |
|
} |
|
} |
|
pagevec_release(&pvec); |
|
cond_resched(); |
|
} |
|
|
|
/* |
|
* If we hit the last page and there is more work to be done: wrap |
|
* back the index back to the start of the file for the next |
|
* time we are called. |
|
*/ |
|
if (wbc->range_cyclic && !done) |
|
done_index = 0; |
|
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
|
mapping->writeback_index = done_index; |
|
|
|
return ret; |
|
} |
|
EXPORT_SYMBOL(write_cache_pages); |
|
|
|
/* |
|
* Function used by generic_writepages to call the real writepage |
|
* function and set the mapping flags on error |
|
*/ |
|
static int __writepage(struct page *page, struct writeback_control *wbc, |
|
void *data) |
|
{ |
|
struct address_space *mapping = data; |
|
int ret = mapping->a_ops->writepage(page, wbc); |
|
mapping_set_error(mapping, ret); |
|
return ret; |
|
} |
|
|
|
/** |
|
* generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
|
* @mapping: address space structure to write |
|
* @wbc: subtract the number of written pages from *@wbc->nr_to_write |
|
* |
|
* This is a library function, which implements the writepages() |
|
* address_space_operation. |
|
* |
|
* Return: %0 on success, negative error code otherwise |
|
*/ |
|
int generic_writepages(struct address_space *mapping, |
|
struct writeback_control *wbc) |
|
{ |
|
struct blk_plug plug; |
|
int ret; |
|
|
|
/* deal with chardevs and other special file */ |
|
if (!mapping->a_ops->writepage) |
|
return 0; |
|
|
|
blk_start_plug(&plug); |
|
ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
|
blk_finish_plug(&plug); |
|
return ret; |
|
} |
|
|
|
EXPORT_SYMBOL(generic_writepages); |
|
|
|
int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
|
{ |
|
int ret; |
|
struct bdi_writeback *wb; |
|
|
|
if (wbc->nr_to_write <= 0) |
|
return 0; |
|
wb = inode_to_wb_wbc(mapping->host, wbc); |
|
wb_bandwidth_estimate_start(wb); |
|
while (1) { |
|
if (mapping->a_ops->writepages) |
|
ret = mapping->a_ops->writepages(mapping, wbc); |
|
else |
|
ret = generic_writepages(mapping, wbc); |
|
if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL)) |
|
break; |
|
|
|
/* |
|
* Lacking an allocation context or the locality or writeback |
|
* state of any of the inode's pages, throttle based on |
|
* writeback activity on the local node. It's as good a |
|
* guess as any. |
|
*/ |
|
reclaim_throttle(NODE_DATA(numa_node_id()), |
|
VMSCAN_THROTTLE_WRITEBACK); |
|
} |
|
/* |
|
* Usually few pages are written by now from those we've just submitted |
|
* but if there's constant writeback being submitted, this makes sure |
|
* writeback bandwidth is updated once in a while. |
|
*/ |
|
if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + |
|
BANDWIDTH_INTERVAL)) |
|
wb_update_bandwidth(wb); |
|
return ret; |
|
} |
|
|
|
/** |
|
* folio_write_one - write out a single folio and wait on I/O. |
|
* @folio: The folio to write. |
|
* |
|
* The folio must be locked by the caller and will be unlocked upon return. |
|
* |
|
* Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this |
|
* function returns. |
|
* |
|
* Return: %0 on success, negative error code otherwise |
|
*/ |
|
int folio_write_one(struct folio *folio) |
|
{ |
|
struct address_space *mapping = folio->mapping; |
|
int ret = 0; |
|
struct writeback_control wbc = { |
|
.sync_mode = WB_SYNC_ALL, |
|
.nr_to_write = folio_nr_pages(folio), |
|
}; |
|
|
|
BUG_ON(!folio_test_locked(folio)); |
|
|
|
folio_wait_writeback(folio); |
|
|
|
if (folio_clear_dirty_for_io(folio)) { |
|
folio_get(folio); |
|
ret = mapping->a_ops->writepage(&folio->page, &wbc); |
|
if (ret == 0) |
|
folio_wait_writeback(folio); |
|
folio_put(folio); |
|
} else { |
|
folio_unlock(folio); |
|
} |
|
|
|
if (!ret) |
|
ret = filemap_check_errors(mapping); |
|
return ret; |
|
} |
|
EXPORT_SYMBOL(folio_write_one); |
|
|
|
/* |
|
* For address_spaces which do not use buffers nor write back. |
|
*/ |
|
bool noop_dirty_folio(struct address_space *mapping, struct folio *folio) |
|
{ |
|
if (!folio_test_dirty(folio)) |
|
return !folio_test_set_dirty(folio); |
|
return false; |
|
} |
|
EXPORT_SYMBOL(noop_dirty_folio); |
|
|
|
/* |
|
* Helper function for set_page_dirty family. |
|
* |
|
* Caller must hold lock_page_memcg(). |
|
* |
|
* NOTE: This relies on being atomic wrt interrupts. |
|
*/ |
|
static void folio_account_dirtied(struct folio *folio, |
|
struct address_space *mapping) |
|
{ |
|
struct inode *inode = mapping->host; |
|
|
|
trace_writeback_dirty_folio(folio, mapping); |
|
|
|
if (mapping_can_writeback(mapping)) { |
|
struct bdi_writeback *wb; |
|
long nr = folio_nr_pages(folio); |
|
|
|
inode_attach_wb(inode, &folio->page); |
|
wb = inode_to_wb(inode); |
|
|
|
__lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr); |
|
__zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr); |
|
__node_stat_mod_folio(folio, NR_DIRTIED, nr); |
|
wb_stat_mod(wb, WB_RECLAIMABLE, nr); |
|
wb_stat_mod(wb, WB_DIRTIED, nr); |
|
task_io_account_write(nr * PAGE_SIZE); |
|
current->nr_dirtied += nr; |
|
__this_cpu_add(bdp_ratelimits, nr); |
|
|
|
mem_cgroup_track_foreign_dirty(folio, wb); |
|
} |
|
} |
|
|
|
/* |
|
* Helper function for deaccounting dirty page without writeback. |
|
* |
|
* Caller must hold lock_page_memcg(). |
|
*/ |
|
void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb) |
|
{ |
|
long nr = folio_nr_pages(folio); |
|
|
|
lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr); |
|
zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); |
|
wb_stat_mod(wb, WB_RECLAIMABLE, -nr); |
|
task_io_account_cancelled_write(nr * PAGE_SIZE); |
|
} |
|
|
|
/* |
|
* Mark the folio dirty, and set it dirty in the page cache, and mark |
|
* the inode dirty. |
|
* |
|
* If warn is true, then emit a warning if the folio is not uptodate and has |
|
* not been truncated. |
|
* |
|
* The caller must hold lock_page_memcg(). Most callers have the folio |
|
* locked. A few have the folio blocked from truncation through other |
|
* means (eg zap_page_range() has it mapped and is holding the page table |
|
* lock). This can also be called from mark_buffer_dirty(), which I |
|
* cannot prove is always protected against truncate. |
|
*/ |
|
void __folio_mark_dirty(struct folio *folio, struct address_space *mapping, |
|
int warn) |
|
{ |
|
unsigned long flags; |
|
|
|
xa_lock_irqsave(&mapping->i_pages, flags); |
|
if (folio->mapping) { /* Race with truncate? */ |
|
WARN_ON_ONCE(warn && !folio_test_uptodate(folio)); |
|
folio_account_dirtied(folio, mapping); |
|
__xa_set_mark(&mapping->i_pages, folio_index(folio), |
|
PAGECACHE_TAG_DIRTY); |
|
} |
|
xa_unlock_irqrestore(&mapping->i_pages, flags); |
|
} |
|
|
|
/** |
|
* filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads. |
|
* @mapping: Address space this folio belongs to. |
|
* @folio: Folio to be marked as dirty. |
|
* |
|
* Filesystems which do not use buffer heads should call this function |
|
* from their set_page_dirty address space operation. It ignores the |
|
* contents of folio_get_private(), so if the filesystem marks individual |
|
* blocks as dirty, the filesystem should handle that itself. |
|
* |
|
* This is also sometimes used by filesystems which use buffer_heads when |
|
* a single buffer is being dirtied: we want to set the folio dirty in |
|
* that case, but not all the buffers. This is a "bottom-up" dirtying, |
|
* whereas block_dirty_folio() is a "top-down" dirtying. |
|
* |
|
* The caller must ensure this doesn't race with truncation. Most will |
|
* simply hold the folio lock, but e.g. zap_pte_range() calls with the |
|
* folio mapped and the pte lock held, which also locks out truncation. |
|
*/ |
|
bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio) |
|
{ |
|
folio_memcg_lock(folio); |
|
if (folio_test_set_dirty(folio)) { |
|
folio_memcg_unlock(folio); |
|
return false; |
|
} |
|
|
|
__folio_mark_dirty(folio, mapping, !folio_test_private(folio)); |
|
folio_memcg_unlock(folio); |
|
|
|
if (mapping->host) { |
|
/* !PageAnon && !swapper_space */ |
|
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
|
} |
|
return true; |
|
} |
|
EXPORT_SYMBOL(filemap_dirty_folio); |
|
|
|
/** |
|
* folio_account_redirty - Manually account for redirtying a page. |
|
* @folio: The folio which is being redirtied. |
|
* |
|
* Most filesystems should call folio_redirty_for_writepage() instead |
|
* of this fuction. If your filesystem is doing writeback outside the |
|
* context of a writeback_control(), it can call this when redirtying |
|
* a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED, |
|
* tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN, |
|
* WB_WRITTEN) in long term. The mismatches will lead to systematic errors |
|
* in balanced_dirty_ratelimit and the dirty pages position control. |
|
*/ |
|
void folio_account_redirty(struct folio *folio) |
|
{ |
|
struct address_space *mapping = folio->mapping; |
|
|
|
if (mapping && mapping_can_writeback(mapping)) { |
|
struct inode *inode = mapping->host; |
|
struct bdi_writeback *wb; |
|
struct wb_lock_cookie cookie = {}; |
|
long nr = folio_nr_pages(folio); |
|
|
|
wb = unlocked_inode_to_wb_begin(inode, &cookie); |
|
current->nr_dirtied -= nr; |
|
node_stat_mod_folio(folio, NR_DIRTIED, -nr); |
|
wb_stat_mod(wb, WB_DIRTIED, -nr); |
|
unlocked_inode_to_wb_end(inode, &cookie); |
|
} |
|
} |
|
EXPORT_SYMBOL(folio_account_redirty); |
|
|
|
/** |
|
* folio_redirty_for_writepage - Decline to write a dirty folio. |
|
* @wbc: The writeback control. |
|
* @folio: The folio. |
|
* |
|
* When a writepage implementation decides that it doesn't want to write |
|
* @folio for some reason, it should call this function, unlock @folio and |
|
* return 0. |
|
* |
|
* Return: True if we redirtied the folio. False if someone else dirtied |
|
* it first. |
|
*/ |
|
bool folio_redirty_for_writepage(struct writeback_control *wbc, |
|
struct folio *folio) |
|
{ |
|
bool ret; |
|
long nr = folio_nr_pages(folio); |
|
|
|
wbc->pages_skipped += nr; |
|
ret = filemap_dirty_folio(folio->mapping, folio); |
|
folio_account_redirty(folio); |
|
|
|
return ret; |
|
} |
|
EXPORT_SYMBOL(folio_redirty_for_writepage); |
|
|
|
/** |
|
* folio_mark_dirty - Mark a folio as being modified. |
|
* @folio: The folio. |
|
* |
|
* The folio may not be truncated while this function is running. |
|
* Holding the folio lock is sufficient to prevent truncation, but some |
|
* callers cannot acquire a sleeping lock. These callers instead hold |
|
* the page table lock for a page table which contains at least one page |
|
* in this folio. Truncation will block on the page table lock as it |
|
* unmaps pages before removing the folio from its mapping. |
|
* |
|
* Return: True if the folio was newly dirtied, false if it was already dirty. |
|
*/ |
|
bool folio_mark_dirty(struct folio *folio) |
|
{ |
|
struct address_space *mapping = folio_mapping(folio); |
|
|
|
if (likely(mapping)) { |
|
/* |
|
* readahead/lru_deactivate_page could remain |
|
* PG_readahead/PG_reclaim due to race with folio_end_writeback |
|
* About readahead, if the folio is written, the flags would be |
|
* reset. So no problem. |
|
* About lru_deactivate_page, if the folio is redirtied, |
|
* the flag will be reset. So no problem. but if the |
|
* folio is used by readahead it will confuse readahead |
|
* and make it restart the size rampup process. But it's |
|
* a trivial problem. |
|
*/ |
|
if (folio_test_reclaim(folio)) |
|
folio_clear_reclaim(folio); |
|
return mapping->a_ops->dirty_folio(mapping, folio); |
|
} |
|
|
|
return noop_dirty_folio(mapping, folio); |
|
} |
|
EXPORT_SYMBOL(folio_mark_dirty); |
|
|
|
/* |
|
* set_page_dirty() is racy if the caller has no reference against |
|
* page->mapping->host, and if the page is unlocked. This is because another |
|
* CPU could truncate the page off the mapping and then free the mapping. |
|
* |
|
* Usually, the page _is_ locked, or the caller is a user-space process which |
|
* holds a reference on the inode by having an open file. |
|
* |
|
* In other cases, the page should be locked before running set_page_dirty(). |
|
*/ |
|
int set_page_dirty_lock(struct page *page) |
|
{ |
|
int ret; |
|
|
|
lock_page(page); |
|
ret = set_page_dirty(page); |
|
unlock_page(page); |
|
return ret; |
|
} |
|
EXPORT_SYMBOL(set_page_dirty_lock); |
|
|
|
/* |
|
* This cancels just the dirty bit on the kernel page itself, it does NOT |
|
* actually remove dirty bits on any mmap's that may be around. It also |
|
* leaves the page tagged dirty, so any sync activity will still find it on |
|
* the dirty lists, and in particular, clear_page_dirty_for_io() will still |
|
* look at the dirty bits in the VM. |
|
* |
|
* Doing this should *normally* only ever be done when a page is truncated, |
|
* and is not actually mapped anywhere at all. However, fs/buffer.c does |
|
* this when it notices that somebody has cleaned out all the buffers on a |
|
* page without actually doing it through the VM. Can you say "ext3 is |
|
* horribly ugly"? Thought you could. |
|
*/ |
|
void __folio_cancel_dirty(struct folio *folio) |
|
{ |
|
struct address_space *mapping = folio_mapping(folio); |
|
|
|
if (mapping_can_writeback(mapping)) { |
|
struct inode *inode = mapping->host; |
|
struct bdi_writeback *wb; |
|
struct wb_lock_cookie cookie = {}; |
|
|
|
folio_memcg_lock(folio); |
|
wb = unlocked_inode_to_wb_begin(inode, &cookie); |
|
|
|
if (folio_test_clear_dirty(folio)) |
|
folio_account_cleaned(folio, wb); |
|
|
|
unlocked_inode_to_wb_end(inode, &cookie); |
|
folio_memcg_unlock(folio); |
|
} else { |
|
folio_clear_dirty(folio); |
|
} |
|
} |
|
EXPORT_SYMBOL(__folio_cancel_dirty); |
|
|
|
/* |
|
* Clear a folio's dirty flag, while caring for dirty memory accounting. |
|
* Returns true if the folio was previously dirty. |
|
* |
|
* This is for preparing to put the folio under writeout. We leave |
|
* the folio tagged as dirty in the xarray so that a concurrent |
|
* write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk. |
|
* The ->writepage implementation will run either folio_start_writeback() |
|
* or folio_mark_dirty(), at which stage we bring the folio's dirty flag |
|
* and xarray dirty tag back into sync. |
|
* |
|
* This incoherency between the folio's dirty flag and xarray tag is |
|
* unfortunate, but it only exists while the folio is locked. |
|
*/ |
|
bool folio_clear_dirty_for_io(struct folio *folio) |
|
{ |
|
struct address_space *mapping = folio_mapping(folio); |
|
bool ret = false; |
|
|
|
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); |
|
|
|
if (mapping && mapping_can_writeback(mapping)) { |
|
struct inode *inode = mapping->host; |
|
struct bdi_writeback *wb; |
|
struct wb_lock_cookie cookie = {}; |
|
|
|
/* |
|
* Yes, Virginia, this is indeed insane. |
|
* |
|
* We use this sequence to make sure that |
|
* (a) we account for dirty stats properly |
|
* (b) we tell the low-level filesystem to |
|
* mark the whole folio dirty if it was |
|
* dirty in a pagetable. Only to then |
|
* (c) clean the folio again and return 1 to |
|
* cause the writeback. |
|
* |
|
* This way we avoid all nasty races with the |
|
* dirty bit in multiple places and clearing |
|
* them concurrently from different threads. |
|
* |
|
* Note! Normally the "folio_mark_dirty(folio)" |
|
* has no effect on the actual dirty bit - since |
|
* that will already usually be set. But we |
|
* need the side effects, and it can help us |
|
* avoid races. |
|
* |
|
* We basically use the folio "master dirty bit" |
|
* as a serialization point for all the different |
|
* threads doing their things. |
|
*/ |
|
if (folio_mkclean(folio)) |
|
folio_mark_dirty(folio); |
|
/* |
|
* We carefully synchronise fault handlers against |
|
* installing a dirty pte and marking the folio dirty |
|
* at this point. We do this by having them hold the |
|
* page lock while dirtying the folio, and folios are |
|
* always locked coming in here, so we get the desired |
|
* exclusion. |
|
*/ |
|
wb = unlocked_inode_to_wb_begin(inode, &cookie); |
|
if (folio_test_clear_dirty(folio)) { |
|
long nr = folio_nr_pages(folio); |
|
lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr); |
|
zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); |
|
wb_stat_mod(wb, WB_RECLAIMABLE, -nr); |
|
ret = true; |
|
} |
|
unlocked_inode_to_wb_end(inode, &cookie); |
|
return ret; |
|
} |
|
return folio_test_clear_dirty(folio); |
|
} |
|
EXPORT_SYMBOL(folio_clear_dirty_for_io); |
|
|
|
static void wb_inode_writeback_start(struct bdi_writeback *wb) |
|
{ |
|
atomic_inc(&wb->writeback_inodes); |
|
} |
|
|
|
static void wb_inode_writeback_end(struct bdi_writeback *wb) |
|
{ |
|
unsigned long flags; |
|
atomic_dec(&wb->writeback_inodes); |
|
/* |
|
* Make sure estimate of writeback throughput gets updated after |
|
* writeback completed. We delay the update by BANDWIDTH_INTERVAL |
|
* (which is the interval other bandwidth updates use for batching) so |
|
* that if multiple inodes end writeback at a similar time, they get |
|
* batched into one bandwidth update. |
|
*/ |
|
spin_lock_irqsave(&wb->work_lock, flags); |
|
if (test_bit(WB_registered, &wb->state)) |
|
queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL); |
|
spin_unlock_irqrestore(&wb->work_lock, flags); |
|
} |
|
|
|
bool __folio_end_writeback(struct folio *folio) |
|
{ |
|
long nr = folio_nr_pages(folio); |
|
struct address_space *mapping = folio_mapping(folio); |
|
bool ret; |
|
|
|
folio_memcg_lock(folio); |
|
if (mapping && mapping_use_writeback_tags(mapping)) { |
|
struct inode *inode = mapping->host; |
|
struct backing_dev_info *bdi = inode_to_bdi(inode); |
|
unsigned long flags; |
|
|
|
xa_lock_irqsave(&mapping->i_pages, flags); |
|
ret = folio_test_clear_writeback(folio); |
|
if (ret) { |
|
__xa_clear_mark(&mapping->i_pages, folio_index(folio), |
|
PAGECACHE_TAG_WRITEBACK); |
|
if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) { |
|
struct bdi_writeback *wb = inode_to_wb(inode); |
|
|
|
wb_stat_mod(wb, WB_WRITEBACK, -nr); |
|
__wb_writeout_add(wb, nr); |
|
if (!mapping_tagged(mapping, |
|
PAGECACHE_TAG_WRITEBACK)) |
|
wb_inode_writeback_end(wb); |
|
} |
|
} |
|
|
|
if (mapping->host && !mapping_tagged(mapping, |
|
PAGECACHE_TAG_WRITEBACK)) |
|
sb_clear_inode_writeback(mapping->host); |
|
|
|
xa_unlock_irqrestore(&mapping->i_pages, flags); |
|
} else { |
|
ret = folio_test_clear_writeback(folio); |
|
} |
|
if (ret) { |
|
lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr); |
|
zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); |
|
node_stat_mod_folio(folio, NR_WRITTEN, nr); |
|
} |
|
folio_memcg_unlock(folio); |
|
return ret; |
|
} |
|
|
|
bool __folio_start_writeback(struct folio *folio, bool keep_write) |
|
{ |
|
long nr = folio_nr_pages(folio); |
|
struct address_space *mapping = folio_mapping(folio); |
|
bool ret; |
|
int access_ret; |
|
|
|
folio_memcg_lock(folio); |
|
if (mapping && mapping_use_writeback_tags(mapping)) { |
|
XA_STATE(xas, &mapping->i_pages, folio_index(folio)); |
|
struct inode *inode = mapping->host; |
|
struct backing_dev_info *bdi = inode_to_bdi(inode); |
|
unsigned long flags; |
|
|
|
xas_lock_irqsave(&xas, flags); |
|
xas_load(&xas); |
|
ret = folio_test_set_writeback(folio); |
|
if (!ret) { |
|
bool on_wblist; |
|
|
|
on_wblist = mapping_tagged(mapping, |
|
PAGECACHE_TAG_WRITEBACK); |
|
|
|
xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK); |
|
if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) { |
|
struct bdi_writeback *wb = inode_to_wb(inode); |
|
|
|
wb_stat_mod(wb, WB_WRITEBACK, nr); |
|
if (!on_wblist) |
|
wb_inode_writeback_start(wb); |
|
} |
|
|
|
/* |
|
* We can come through here when swapping |
|
* anonymous folios, so we don't necessarily |
|
* have an inode to track for sync. |
|
*/ |
|
if (mapping->host && !on_wblist) |
|
sb_mark_inode_writeback(mapping->host); |
|
} |
|
if (!folio_test_dirty(folio)) |
|
xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY); |
|
if (!keep_write) |
|
xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE); |
|
xas_unlock_irqrestore(&xas, flags); |
|
} else { |
|
ret = folio_test_set_writeback(folio); |
|
} |
|
if (!ret) { |
|
lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr); |
|
zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr); |
|
} |
|
folio_memcg_unlock(folio); |
|
access_ret = arch_make_folio_accessible(folio); |
|
/* |
|
* If writeback has been triggered on a page that cannot be made |
|
* accessible, it is too late to recover here. |
|
*/ |
|
VM_BUG_ON_FOLIO(access_ret != 0, folio); |
|
|
|
return ret; |
|
} |
|
EXPORT_SYMBOL(__folio_start_writeback); |
|
|
|
/** |
|
* folio_wait_writeback - Wait for a folio to finish writeback. |
|
* @folio: The folio to wait for. |
|
* |
|
* If the folio is currently being written back to storage, wait for the |
|
* I/O to complete. |
|
* |
|
* Context: Sleeps. Must be called in process context and with |
|
* no spinlocks held. Caller should hold a reference on the folio. |
|
* If the folio is not locked, writeback may start again after writeback |
|
* has finished. |
|
*/ |
|
void folio_wait_writeback(struct folio *folio) |
|
{ |
|
while (folio_test_writeback(folio)) { |
|
trace_folio_wait_writeback(folio, folio_mapping(folio)); |
|
folio_wait_bit(folio, PG_writeback); |
|
} |
|
} |
|
EXPORT_SYMBOL_GPL(folio_wait_writeback); |
|
|
|
/** |
|
* folio_wait_writeback_killable - Wait for a folio to finish writeback. |
|
* @folio: The folio to wait for. |
|
* |
|
* If the folio is currently being written back to storage, wait for the |
|
* I/O to complete or a fatal signal to arrive. |
|
* |
|
* Context: Sleeps. Must be called in process context and with |
|
* no spinlocks held. Caller should hold a reference on the folio. |
|
* If the folio is not locked, writeback may start again after writeback |
|
* has finished. |
|
* Return: 0 on success, -EINTR if we get a fatal signal while waiting. |
|
*/ |
|
int folio_wait_writeback_killable(struct folio *folio) |
|
{ |
|
while (folio_test_writeback(folio)) { |
|
trace_folio_wait_writeback(folio, folio_mapping(folio)); |
|
if (folio_wait_bit_killable(folio, PG_writeback)) |
|
return -EINTR; |
|
} |
|
|
|
return 0; |
|
} |
|
EXPORT_SYMBOL_GPL(folio_wait_writeback_killable); |
|
|
|
/** |
|
* folio_wait_stable() - wait for writeback to finish, if necessary. |
|
* @folio: The folio to wait on. |
|
* |
|
* This function determines if the given folio is related to a backing |
|
* device that requires folio contents to be held stable during writeback. |
|
* If so, then it will wait for any pending writeback to complete. |
|
* |
|
* Context: Sleeps. Must be called in process context and with |
|
* no spinlocks held. Caller should hold a reference on the folio. |
|
* If the folio is not locked, writeback may start again after writeback |
|
* has finished. |
|
*/ |
|
void folio_wait_stable(struct folio *folio) |
|
{ |
|
if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES) |
|
folio_wait_writeback(folio); |
|
} |
|
EXPORT_SYMBOL_GPL(folio_wait_stable);
|
|
|