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469 lines
14 KiB
469 lines
14 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Linux VM pressure |
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* |
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* Copyright 2012 Linaro Ltd. |
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* Anton Vorontsov <[email protected]> |
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* |
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* Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro, |
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* Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg. |
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*/ |
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#include <linux/cgroup.h> |
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#include <linux/fs.h> |
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#include <linux/log2.h> |
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#include <linux/sched.h> |
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#include <linux/mm.h> |
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#include <linux/vmstat.h> |
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#include <linux/eventfd.h> |
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#include <linux/slab.h> |
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#include <linux/swap.h> |
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#include <linux/printk.h> |
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#include <linux/vmpressure.h> |
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|
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/* |
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* The window size (vmpressure_win) is the number of scanned pages before |
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* we try to analyze scanned/reclaimed ratio. So the window is used as a |
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* rate-limit tunable for the "low" level notification, and also for |
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* averaging the ratio for medium/critical levels. Using small window |
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* sizes can cause lot of false positives, but too big window size will |
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* delay the notifications. |
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* |
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* As the vmscan reclaimer logic works with chunks which are multiple of |
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* SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well. |
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* |
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* TODO: Make the window size depend on machine size, as we do for vmstat |
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* thresholds. Currently we set it to 512 pages (2MB for 4KB pages). |
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*/ |
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static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16; |
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/* |
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* These thresholds are used when we account memory pressure through |
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* scanned/reclaimed ratio. The current values were chosen empirically. In |
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* essence, they are percents: the higher the value, the more number |
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* unsuccessful reclaims there were. |
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*/ |
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static const unsigned int vmpressure_level_med = 60; |
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static const unsigned int vmpressure_level_critical = 95; |
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|
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/* |
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* When there are too little pages left to scan, vmpressure() may miss the |
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* critical pressure as number of pages will be less than "window size". |
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* However, in that case the vmscan priority will raise fast as the |
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* reclaimer will try to scan LRUs more deeply. |
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* |
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* The vmscan logic considers these special priorities: |
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* |
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* prio == DEF_PRIORITY (12): reclaimer starts with that value |
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* prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed |
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* prio == 0 : close to OOM, kernel scans every page in an lru |
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* |
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* Any value in this range is acceptable for this tunable (i.e. from 12 to |
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* 0). Current value for the vmpressure_level_critical_prio is chosen |
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* empirically, but the number, in essence, means that we consider |
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* critical level when scanning depth is ~10% of the lru size (vmscan |
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* scans 'lru_size >> prio' pages, so it is actually 12.5%, or one |
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* eights). |
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*/ |
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static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10); |
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static struct vmpressure *work_to_vmpressure(struct work_struct *work) |
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{ |
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return container_of(work, struct vmpressure, work); |
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} |
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static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr) |
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{ |
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struct cgroup_subsys_state *css = vmpressure_to_css(vmpr); |
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struct mem_cgroup *memcg = mem_cgroup_from_css(css); |
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memcg = parent_mem_cgroup(memcg); |
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if (!memcg) |
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return NULL; |
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return memcg_to_vmpressure(memcg); |
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} |
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enum vmpressure_levels { |
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VMPRESSURE_LOW = 0, |
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VMPRESSURE_MEDIUM, |
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VMPRESSURE_CRITICAL, |
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VMPRESSURE_NUM_LEVELS, |
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}; |
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enum vmpressure_modes { |
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VMPRESSURE_NO_PASSTHROUGH = 0, |
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VMPRESSURE_HIERARCHY, |
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VMPRESSURE_LOCAL, |
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VMPRESSURE_NUM_MODES, |
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}; |
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static const char * const vmpressure_str_levels[] = { |
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[VMPRESSURE_LOW] = "low", |
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[VMPRESSURE_MEDIUM] = "medium", |
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[VMPRESSURE_CRITICAL] = "critical", |
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}; |
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static const char * const vmpressure_str_modes[] = { |
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[VMPRESSURE_NO_PASSTHROUGH] = "default", |
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[VMPRESSURE_HIERARCHY] = "hierarchy", |
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[VMPRESSURE_LOCAL] = "local", |
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}; |
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static enum vmpressure_levels vmpressure_level(unsigned long pressure) |
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{ |
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if (pressure >= vmpressure_level_critical) |
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return VMPRESSURE_CRITICAL; |
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else if (pressure >= vmpressure_level_med) |
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return VMPRESSURE_MEDIUM; |
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return VMPRESSURE_LOW; |
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} |
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static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, |
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unsigned long reclaimed) |
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{ |
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unsigned long scale = scanned + reclaimed; |
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unsigned long pressure = 0; |
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/* |
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* reclaimed can be greater than scanned for things such as reclaimed |
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* slab pages. shrink_node() just adds reclaimed pages without a |
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* related increment to scanned pages. |
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*/ |
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if (reclaimed >= scanned) |
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goto out; |
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/* |
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* We calculate the ratio (in percents) of how many pages were |
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* scanned vs. reclaimed in a given time frame (window). Note that |
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* time is in VM reclaimer's "ticks", i.e. number of pages |
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* scanned. This makes it possible to set desired reaction time |
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* and serves as a ratelimit. |
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*/ |
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pressure = scale - (reclaimed * scale / scanned); |
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pressure = pressure * 100 / scale; |
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out: |
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pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure, |
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scanned, reclaimed); |
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return vmpressure_level(pressure); |
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} |
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struct vmpressure_event { |
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struct eventfd_ctx *efd; |
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enum vmpressure_levels level; |
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enum vmpressure_modes mode; |
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struct list_head node; |
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}; |
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static bool vmpressure_event(struct vmpressure *vmpr, |
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const enum vmpressure_levels level, |
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bool ancestor, bool signalled) |
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{ |
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struct vmpressure_event *ev; |
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bool ret = false; |
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mutex_lock(&vmpr->events_lock); |
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list_for_each_entry(ev, &vmpr->events, node) { |
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if (ancestor && ev->mode == VMPRESSURE_LOCAL) |
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continue; |
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if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH) |
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continue; |
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if (level < ev->level) |
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continue; |
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eventfd_signal(ev->efd, 1); |
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ret = true; |
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} |
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mutex_unlock(&vmpr->events_lock); |
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return ret; |
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} |
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static void vmpressure_work_fn(struct work_struct *work) |
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{ |
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struct vmpressure *vmpr = work_to_vmpressure(work); |
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unsigned long scanned; |
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unsigned long reclaimed; |
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enum vmpressure_levels level; |
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bool ancestor = false; |
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bool signalled = false; |
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spin_lock(&vmpr->sr_lock); |
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/* |
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* Several contexts might be calling vmpressure(), so it is |
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* possible that the work was rescheduled again before the old |
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* work context cleared the counters. In that case we will run |
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* just after the old work returns, but then scanned might be zero |
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* here. No need for any locks here since we don't care if |
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* vmpr->reclaimed is in sync. |
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*/ |
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scanned = vmpr->tree_scanned; |
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if (!scanned) { |
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spin_unlock(&vmpr->sr_lock); |
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return; |
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} |
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reclaimed = vmpr->tree_reclaimed; |
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vmpr->tree_scanned = 0; |
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vmpr->tree_reclaimed = 0; |
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spin_unlock(&vmpr->sr_lock); |
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level = vmpressure_calc_level(scanned, reclaimed); |
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do { |
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if (vmpressure_event(vmpr, level, ancestor, signalled)) |
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signalled = true; |
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ancestor = true; |
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} while ((vmpr = vmpressure_parent(vmpr))); |
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} |
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/** |
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* vmpressure() - Account memory pressure through scanned/reclaimed ratio |
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* @gfp: reclaimer's gfp mask |
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* @memcg: cgroup memory controller handle |
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* @tree: legacy subtree mode |
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* @scanned: number of pages scanned |
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* @reclaimed: number of pages reclaimed |
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* |
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* This function should be called from the vmscan reclaim path to account |
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* "instantaneous" memory pressure (scanned/reclaimed ratio). The raw |
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* pressure index is then further refined and averaged over time. |
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* |
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* If @tree is set, vmpressure is in traditional userspace reporting |
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* mode: @memcg is considered the pressure root and userspace is |
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* notified of the entire subtree's reclaim efficiency. |
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* |
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* If @tree is not set, reclaim efficiency is recorded for @memcg, and |
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* only in-kernel users are notified. |
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* |
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* This function does not return any value. |
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*/ |
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void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree, |
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unsigned long scanned, unsigned long reclaimed) |
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{ |
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg); |
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/* |
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* Here we only want to account pressure that userland is able to |
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* help us with. For example, suppose that DMA zone is under |
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* pressure; if we notify userland about that kind of pressure, |
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* then it will be mostly a waste as it will trigger unnecessary |
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* freeing of memory by userland (since userland is more likely to |
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* have HIGHMEM/MOVABLE pages instead of the DMA fallback). That |
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* is why we include only movable, highmem and FS/IO pages. |
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* Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so |
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* we account it too. |
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*/ |
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if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS))) |
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return; |
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/* |
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* If we got here with no pages scanned, then that is an indicator |
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* that reclaimer was unable to find any shrinkable LRUs at the |
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* current scanning depth. But it does not mean that we should |
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* report the critical pressure, yet. If the scanning priority |
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* (scanning depth) goes too high (deep), we will be notified |
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* through vmpressure_prio(). But so far, keep calm. |
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*/ |
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if (!scanned) |
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return; |
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if (tree) { |
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spin_lock(&vmpr->sr_lock); |
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scanned = vmpr->tree_scanned += scanned; |
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vmpr->tree_reclaimed += reclaimed; |
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spin_unlock(&vmpr->sr_lock); |
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if (scanned < vmpressure_win) |
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return; |
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schedule_work(&vmpr->work); |
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} else { |
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enum vmpressure_levels level; |
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/* For now, no users for root-level efficiency */ |
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if (!memcg || mem_cgroup_is_root(memcg)) |
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return; |
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spin_lock(&vmpr->sr_lock); |
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scanned = vmpr->scanned += scanned; |
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reclaimed = vmpr->reclaimed += reclaimed; |
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if (scanned < vmpressure_win) { |
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spin_unlock(&vmpr->sr_lock); |
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return; |
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} |
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vmpr->scanned = vmpr->reclaimed = 0; |
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spin_unlock(&vmpr->sr_lock); |
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level = vmpressure_calc_level(scanned, reclaimed); |
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if (level > VMPRESSURE_LOW) { |
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/* |
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* Let the socket buffer allocator know that |
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* we are having trouble reclaiming LRU pages. |
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* |
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* For hysteresis keep the pressure state |
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* asserted for a second in which subsequent |
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* pressure events can occur. |
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*/ |
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memcg->socket_pressure = jiffies + HZ; |
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} |
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} |
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} |
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/** |
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* vmpressure_prio() - Account memory pressure through reclaimer priority level |
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* @gfp: reclaimer's gfp mask |
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* @memcg: cgroup memory controller handle |
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* @prio: reclaimer's priority |
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* |
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* This function should be called from the reclaim path every time when |
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* the vmscan's reclaiming priority (scanning depth) changes. |
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* |
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* This function does not return any value. |
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*/ |
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void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio) |
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{ |
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/* |
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* We only use prio for accounting critical level. For more info |
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* see comment for vmpressure_level_critical_prio variable above. |
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*/ |
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if (prio > vmpressure_level_critical_prio) |
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return; |
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/* |
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* OK, the prio is below the threshold, updating vmpressure |
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* information before shrinker dives into long shrinking of long |
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* range vmscan. Passing scanned = vmpressure_win, reclaimed = 0 |
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* to the vmpressure() basically means that we signal 'critical' |
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* level. |
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*/ |
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vmpressure(gfp, memcg, true, vmpressure_win, 0); |
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} |
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#define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2) |
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/** |
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* vmpressure_register_event() - Bind vmpressure notifications to an eventfd |
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* @memcg: memcg that is interested in vmpressure notifications |
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* @eventfd: eventfd context to link notifications with |
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* @args: event arguments (pressure level threshold, optional mode) |
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* |
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* This function associates eventfd context with the vmpressure |
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* infrastructure, so that the notifications will be delivered to the |
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* @eventfd. The @args parameter is a comma-delimited string that denotes a |
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* pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium", |
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* or "critical") and an optional mode (one of vmpressure_str_modes, i.e. |
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* "hierarchy" or "local"). |
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* |
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* To be used as memcg event method. |
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* |
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* Return: 0 on success, -ENOMEM on memory failure or -EINVAL if @args could |
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* not be parsed. |
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*/ |
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int vmpressure_register_event(struct mem_cgroup *memcg, |
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struct eventfd_ctx *eventfd, const char *args) |
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{ |
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg); |
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struct vmpressure_event *ev; |
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enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH; |
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enum vmpressure_levels level; |
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char *spec, *spec_orig; |
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char *token; |
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int ret = 0; |
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spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL); |
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if (!spec) |
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return -ENOMEM; |
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/* Find required level */ |
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token = strsep(&spec, ","); |
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ret = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token); |
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if (ret < 0) |
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goto out; |
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level = ret; |
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/* Find optional mode */ |
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token = strsep(&spec, ","); |
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if (token) { |
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ret = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token); |
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if (ret < 0) |
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goto out; |
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mode = ret; |
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} |
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ev = kzalloc(sizeof(*ev), GFP_KERNEL); |
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if (!ev) { |
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ret = -ENOMEM; |
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goto out; |
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} |
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ev->efd = eventfd; |
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ev->level = level; |
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ev->mode = mode; |
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mutex_lock(&vmpr->events_lock); |
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list_add(&ev->node, &vmpr->events); |
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mutex_unlock(&vmpr->events_lock); |
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ret = 0; |
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out: |
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kfree(spec_orig); |
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return ret; |
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} |
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/** |
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* vmpressure_unregister_event() - Unbind eventfd from vmpressure |
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* @memcg: memcg handle |
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* @eventfd: eventfd context that was used to link vmpressure with the @cg |
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* |
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* This function does internal manipulations to detach the @eventfd from |
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* the vmpressure notifications, and then frees internal resources |
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* associated with the @eventfd (but the @eventfd itself is not freed). |
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* |
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* To be used as memcg event method. |
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*/ |
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void vmpressure_unregister_event(struct mem_cgroup *memcg, |
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struct eventfd_ctx *eventfd) |
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{ |
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg); |
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struct vmpressure_event *ev; |
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mutex_lock(&vmpr->events_lock); |
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list_for_each_entry(ev, &vmpr->events, node) { |
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if (ev->efd != eventfd) |
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continue; |
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list_del(&ev->node); |
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kfree(ev); |
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break; |
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} |
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mutex_unlock(&vmpr->events_lock); |
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} |
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/** |
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* vmpressure_init() - Initialize vmpressure control structure |
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* @vmpr: Structure to be initialized |
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* |
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* This function should be called on every allocated vmpressure structure |
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* before any usage. |
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*/ |
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void vmpressure_init(struct vmpressure *vmpr) |
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{ |
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spin_lock_init(&vmpr->sr_lock); |
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mutex_init(&vmpr->events_lock); |
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INIT_LIST_HEAD(&vmpr->events); |
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INIT_WORK(&vmpr->work, vmpressure_work_fn); |
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} |
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/** |
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* vmpressure_cleanup() - shuts down vmpressure control structure |
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* @vmpr: Structure to be cleaned up |
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* |
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* This function should be called before the structure in which it is |
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* embedded is cleaned up. |
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*/ |
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void vmpressure_cleanup(struct vmpressure *vmpr) |
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{ |
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/* |
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* Make sure there is no pending work before eventfd infrastructure |
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* goes away. |
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*/ |
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flush_work(&vmpr->work); |
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}
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