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717 lines
20 KiB
717 lines
20 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* mm/readahead.c - address_space-level file readahead. |
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* |
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* Copyright (C) 2002, Linus Torvalds |
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* |
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* 09Apr2002 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/dax.h> |
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#include <linux/gfp.h> |
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#include <linux/export.h> |
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#include <linux/blkdev.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/pagevec.h> |
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#include <linux/pagemap.h> |
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#include <linux/syscalls.h> |
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#include <linux/file.h> |
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#include <linux/mm_inline.h> |
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#include <linux/blk-cgroup.h> |
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#include <linux/fadvise.h> |
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#include <linux/sched/mm.h> |
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|
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#include "internal.h" |
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|
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/* |
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* Initialise a struct file's readahead state. Assumes that the caller has |
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* memset *ra to zero. |
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*/ |
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void |
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file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) |
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{ |
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ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages; |
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ra->prev_pos = -1; |
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} |
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EXPORT_SYMBOL_GPL(file_ra_state_init); |
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|
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/* |
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* see if a page needs releasing upon read_cache_pages() failure |
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* - the caller of read_cache_pages() may have set PG_private or PG_fscache |
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* before calling, such as the NFS fs marking pages that are cached locally |
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* on disk, thus we need to give the fs a chance to clean up in the event of |
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* an error |
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*/ |
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static void read_cache_pages_invalidate_page(struct address_space *mapping, |
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struct page *page) |
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{ |
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if (page_has_private(page)) { |
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if (!trylock_page(page)) |
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BUG(); |
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page->mapping = mapping; |
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do_invalidatepage(page, 0, PAGE_SIZE); |
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page->mapping = NULL; |
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unlock_page(page); |
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} |
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put_page(page); |
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} |
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|
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/* |
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* release a list of pages, invalidating them first if need be |
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*/ |
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static void read_cache_pages_invalidate_pages(struct address_space *mapping, |
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struct list_head *pages) |
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{ |
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struct page *victim; |
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|
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while (!list_empty(pages)) { |
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victim = lru_to_page(pages); |
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list_del(&victim->lru); |
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read_cache_pages_invalidate_page(mapping, victim); |
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} |
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} |
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|
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/** |
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* read_cache_pages - populate an address space with some pages & start reads against them |
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* @mapping: the address_space |
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* @pages: The address of a list_head which contains the target pages. These |
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* pages have their ->index populated and are otherwise uninitialised. |
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* @filler: callback routine for filling a single page. |
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* @data: private data for the callback routine. |
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* |
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* Hides the details of the LRU cache etc from the filesystems. |
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* |
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* Returns: %0 on success, error return by @filler otherwise |
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*/ |
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int read_cache_pages(struct address_space *mapping, struct list_head *pages, |
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int (*filler)(void *, struct page *), void *data) |
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{ |
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struct page *page; |
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int ret = 0; |
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|
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while (!list_empty(pages)) { |
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page = lru_to_page(pages); |
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list_del(&page->lru); |
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if (add_to_page_cache_lru(page, mapping, page->index, |
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readahead_gfp_mask(mapping))) { |
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read_cache_pages_invalidate_page(mapping, page); |
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continue; |
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} |
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put_page(page); |
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|
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ret = filler(data, page); |
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if (unlikely(ret)) { |
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read_cache_pages_invalidate_pages(mapping, pages); |
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break; |
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} |
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task_io_account_read(PAGE_SIZE); |
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} |
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return ret; |
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} |
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|
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EXPORT_SYMBOL(read_cache_pages); |
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|
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static void read_pages(struct readahead_control *rac, struct list_head *pages, |
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bool skip_page) |
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{ |
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const struct address_space_operations *aops = rac->mapping->a_ops; |
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struct page *page; |
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struct blk_plug plug; |
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|
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if (!readahead_count(rac)) |
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goto out; |
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blk_start_plug(&plug); |
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|
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if (aops->readahead) { |
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aops->readahead(rac); |
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/* Clean up the remaining pages */ |
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while ((page = readahead_page(rac))) { |
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unlock_page(page); |
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put_page(page); |
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} |
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} else if (aops->readpages) { |
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aops->readpages(rac->file, rac->mapping, pages, |
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readahead_count(rac)); |
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/* Clean up the remaining pages */ |
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put_pages_list(pages); |
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rac->_index += rac->_nr_pages; |
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rac->_nr_pages = 0; |
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} else { |
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while ((page = readahead_page(rac))) { |
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aops->readpage(rac->file, page); |
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put_page(page); |
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} |
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} |
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blk_finish_plug(&plug); |
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BUG_ON(!list_empty(pages)); |
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BUG_ON(readahead_count(rac)); |
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out: |
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if (skip_page) |
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rac->_index++; |
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} |
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|
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/** |
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* page_cache_ra_unbounded - Start unchecked readahead. |
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* @ractl: Readahead control. |
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* @nr_to_read: The number of pages to read. |
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* @lookahead_size: Where to start the next readahead. |
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* |
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* This function is for filesystems to call when they want to start |
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* readahead beyond a file's stated i_size. This is almost certainly |
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* not the function you want to call. Use page_cache_async_readahead() |
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* or page_cache_sync_readahead() instead. |
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* |
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* Context: File is referenced by caller. Mutexes may be held by caller. |
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* May sleep, but will not reenter filesystem to reclaim memory. |
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*/ |
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void page_cache_ra_unbounded(struct readahead_control *ractl, |
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unsigned long nr_to_read, unsigned long lookahead_size) |
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{ |
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struct address_space *mapping = ractl->mapping; |
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unsigned long index = readahead_index(ractl); |
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LIST_HEAD(page_pool); |
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gfp_t gfp_mask = readahead_gfp_mask(mapping); |
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unsigned long i; |
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|
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/* |
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* Partway through the readahead operation, we will have added |
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* locked pages to the page cache, but will not yet have submitted |
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* them for I/O. Adding another page may need to allocate memory, |
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* which can trigger memory reclaim. Telling the VM we're in |
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* the middle of a filesystem operation will cause it to not |
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* touch file-backed pages, preventing a deadlock. Most (all?) |
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* filesystems already specify __GFP_NOFS in their mapping's |
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* gfp_mask, but let's be explicit here. |
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*/ |
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unsigned int nofs = memalloc_nofs_save(); |
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|
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filemap_invalidate_lock_shared(mapping); |
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/* |
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* Preallocate as many pages as we will need. |
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*/ |
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for (i = 0; i < nr_to_read; i++) { |
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struct page *page = xa_load(&mapping->i_pages, index + i); |
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|
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if (page && !xa_is_value(page)) { |
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/* |
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* Page already present? Kick off the current batch |
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* of contiguous pages before continuing with the |
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* next batch. This page may be the one we would |
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* have intended to mark as Readahead, but we don't |
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* have a stable reference to this page, and it's |
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* not worth getting one just for that. |
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*/ |
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read_pages(ractl, &page_pool, true); |
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i = ractl->_index + ractl->_nr_pages - index - 1; |
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continue; |
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} |
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page = __page_cache_alloc(gfp_mask); |
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if (!page) |
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break; |
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if (mapping->a_ops->readpages) { |
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page->index = index + i; |
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list_add(&page->lru, &page_pool); |
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} else if (add_to_page_cache_lru(page, mapping, index + i, |
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gfp_mask) < 0) { |
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put_page(page); |
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read_pages(ractl, &page_pool, true); |
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i = ractl->_index + ractl->_nr_pages - index - 1; |
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continue; |
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} |
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if (i == nr_to_read - lookahead_size) |
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SetPageReadahead(page); |
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ractl->_nr_pages++; |
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} |
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|
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/* |
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* Now start the IO. We ignore I/O errors - if the page is not |
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* uptodate then the caller will launch readpage again, and |
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* will then handle the error. |
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*/ |
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read_pages(ractl, &page_pool, false); |
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filemap_invalidate_unlock_shared(mapping); |
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memalloc_nofs_restore(nofs); |
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} |
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EXPORT_SYMBOL_GPL(page_cache_ra_unbounded); |
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|
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/* |
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* do_page_cache_ra() actually reads a chunk of disk. It allocates |
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* the pages first, then submits them for I/O. This avoids the very bad |
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* behaviour which would occur if page allocations are causing VM writeback. |
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* We really don't want to intermingle reads and writes like that. |
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*/ |
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void do_page_cache_ra(struct readahead_control *ractl, |
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unsigned long nr_to_read, unsigned long lookahead_size) |
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{ |
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struct inode *inode = ractl->mapping->host; |
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unsigned long index = readahead_index(ractl); |
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loff_t isize = i_size_read(inode); |
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pgoff_t end_index; /* The last page we want to read */ |
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if (isize == 0) |
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return; |
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end_index = (isize - 1) >> PAGE_SHIFT; |
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if (index > end_index) |
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return; |
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/* Don't read past the page containing the last byte of the file */ |
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if (nr_to_read > end_index - index) |
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nr_to_read = end_index - index + 1; |
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page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size); |
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} |
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|
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/* |
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* Chunk the readahead into 2 megabyte units, so that we don't pin too much |
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* memory at once. |
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*/ |
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void force_page_cache_ra(struct readahead_control *ractl, |
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unsigned long nr_to_read) |
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{ |
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struct address_space *mapping = ractl->mapping; |
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struct file_ra_state *ra = ractl->ra; |
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struct backing_dev_info *bdi = inode_to_bdi(mapping->host); |
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unsigned long max_pages, index; |
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|
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if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages && |
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!mapping->a_ops->readahead)) |
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return; |
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/* |
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* If the request exceeds the readahead window, allow the read to |
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* be up to the optimal hardware IO size |
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*/ |
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index = readahead_index(ractl); |
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max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages); |
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nr_to_read = min_t(unsigned long, nr_to_read, max_pages); |
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while (nr_to_read) { |
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unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE; |
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if (this_chunk > nr_to_read) |
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this_chunk = nr_to_read; |
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ractl->_index = index; |
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do_page_cache_ra(ractl, this_chunk, 0); |
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index += this_chunk; |
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nr_to_read -= this_chunk; |
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} |
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} |
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|
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/* |
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* Set the initial window size, round to next power of 2 and square |
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* for small size, x 4 for medium, and x 2 for large |
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* for 128k (32 page) max ra |
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* 1-8 page = 32k initial, > 8 page = 128k initial |
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*/ |
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static unsigned long get_init_ra_size(unsigned long size, unsigned long max) |
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{ |
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unsigned long newsize = roundup_pow_of_two(size); |
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if (newsize <= max / 32) |
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newsize = newsize * 4; |
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else if (newsize <= max / 4) |
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newsize = newsize * 2; |
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else |
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newsize = max; |
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return newsize; |
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} |
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|
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/* |
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* Get the previous window size, ramp it up, and |
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* return it as the new window size. |
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*/ |
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static unsigned long get_next_ra_size(struct file_ra_state *ra, |
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unsigned long max) |
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{ |
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unsigned long cur = ra->size; |
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|
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if (cur < max / 16) |
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return 4 * cur; |
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if (cur <= max / 2) |
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return 2 * cur; |
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return max; |
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} |
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|
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/* |
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* On-demand readahead design. |
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* |
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* The fields in struct file_ra_state represent the most-recently-executed |
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* readahead attempt: |
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* |
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* |<----- async_size ---------| |
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* |------------------- size -------------------->| |
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* |==================#===========================| |
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* ^start ^page marked with PG_readahead |
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* |
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* To overlap application thinking time and disk I/O time, we do |
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* `readahead pipelining': Do not wait until the application consumed all |
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* readahead pages and stalled on the missing page at readahead_index; |
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* Instead, submit an asynchronous readahead I/O as soon as there are |
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* only async_size pages left in the readahead window. Normally async_size |
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* will be equal to size, for maximum pipelining. |
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* |
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* In interleaved sequential reads, concurrent streams on the same fd can |
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* be invalidating each other's readahead state. So we flag the new readahead |
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* page at (start+size-async_size) with PG_readahead, and use it as readahead |
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* indicator. The flag won't be set on already cached pages, to avoid the |
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* readahead-for-nothing fuss, saving pointless page cache lookups. |
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* |
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* prev_pos tracks the last visited byte in the _previous_ read request. |
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* It should be maintained by the caller, and will be used for detecting |
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* small random reads. Note that the readahead algorithm checks loosely |
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* for sequential patterns. Hence interleaved reads might be served as |
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* sequential ones. |
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* |
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* There is a special-case: if the first page which the application tries to |
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* read happens to be the first page of the file, it is assumed that a linear |
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* read is about to happen and the window is immediately set to the initial size |
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* based on I/O request size and the max_readahead. |
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* |
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* The code ramps up the readahead size aggressively at first, but slow down as |
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* it approaches max_readhead. |
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*/ |
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|
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/* |
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* Count contiguously cached pages from @index-1 to @index-@max, |
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* this count is a conservative estimation of |
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* - length of the sequential read sequence, or |
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* - thrashing threshold in memory tight systems |
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*/ |
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static pgoff_t count_history_pages(struct address_space *mapping, |
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pgoff_t index, unsigned long max) |
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{ |
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pgoff_t head; |
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|
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rcu_read_lock(); |
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head = page_cache_prev_miss(mapping, index - 1, max); |
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rcu_read_unlock(); |
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|
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return index - 1 - head; |
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} |
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|
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/* |
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* page cache context based read-ahead |
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*/ |
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static int try_context_readahead(struct address_space *mapping, |
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struct file_ra_state *ra, |
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pgoff_t index, |
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unsigned long req_size, |
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unsigned long max) |
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{ |
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pgoff_t size; |
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size = count_history_pages(mapping, index, max); |
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|
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/* |
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* not enough history pages: |
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* it could be a random read |
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*/ |
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if (size <= req_size) |
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return 0; |
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|
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/* |
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* starts from beginning of file: |
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* it is a strong indication of long-run stream (or whole-file-read) |
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*/ |
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if (size >= index) |
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size *= 2; |
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ra->start = index; |
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ra->size = min(size + req_size, max); |
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ra->async_size = 1; |
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return 1; |
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} |
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/* |
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* A minimal readahead algorithm for trivial sequential/random reads. |
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*/ |
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static void ondemand_readahead(struct readahead_control *ractl, |
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bool hit_readahead_marker, unsigned long req_size) |
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{ |
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struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host); |
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struct file_ra_state *ra = ractl->ra; |
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unsigned long max_pages = ra->ra_pages; |
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unsigned long add_pages; |
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unsigned long index = readahead_index(ractl); |
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pgoff_t prev_index; |
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|
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/* |
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* If the request exceeds the readahead window, allow the read to |
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* be up to the optimal hardware IO size |
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*/ |
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if (req_size > max_pages && bdi->io_pages > max_pages) |
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max_pages = min(req_size, bdi->io_pages); |
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|
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/* |
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* start of file |
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*/ |
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if (!index) |
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goto initial_readahead; |
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|
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/* |
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* It's the expected callback index, assume sequential access. |
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* Ramp up sizes, and push forward the readahead window. |
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*/ |
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if ((index == (ra->start + ra->size - ra->async_size) || |
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index == (ra->start + ra->size))) { |
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ra->start += ra->size; |
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ra->size = get_next_ra_size(ra, max_pages); |
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ra->async_size = ra->size; |
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goto readit; |
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} |
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|
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/* |
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* Hit a marked page without valid readahead state. |
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* E.g. interleaved reads. |
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* Query the pagecache for async_size, which normally equals to |
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* readahead size. Ramp it up and use it as the new readahead size. |
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*/ |
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if (hit_readahead_marker) { |
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pgoff_t start; |
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|
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rcu_read_lock(); |
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start = page_cache_next_miss(ractl->mapping, index + 1, |
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max_pages); |
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rcu_read_unlock(); |
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|
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if (!start || start - index > max_pages) |
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return; |
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|
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ra->start = start; |
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ra->size = start - index; /* old async_size */ |
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ra->size += req_size; |
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ra->size = get_next_ra_size(ra, max_pages); |
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ra->async_size = ra->size; |
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goto readit; |
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} |
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|
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/* |
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* oversize read |
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*/ |
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if (req_size > max_pages) |
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goto initial_readahead; |
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|
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/* |
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* sequential cache miss |
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* trivial case: (index - prev_index) == 1 |
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* unaligned reads: (index - prev_index) == 0 |
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*/ |
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prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT; |
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if (index - prev_index <= 1UL) |
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goto initial_readahead; |
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|
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/* |
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* Query the page cache and look for the traces(cached history pages) |
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* that a sequential stream would leave behind. |
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*/ |
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if (try_context_readahead(ractl->mapping, ra, index, req_size, |
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max_pages)) |
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goto readit; |
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|
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/* |
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* standalone, small random read |
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* Read as is, and do not pollute the readahead state. |
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*/ |
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do_page_cache_ra(ractl, req_size, 0); |
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return; |
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|
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initial_readahead: |
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ra->start = index; |
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ra->size = get_init_ra_size(req_size, max_pages); |
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ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; |
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|
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readit: |
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/* |
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* Will this read hit the readahead marker made by itself? |
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* If so, trigger the readahead marker hit now, and merge |
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* the resulted next readahead window into the current one. |
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* Take care of maximum IO pages as above. |
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*/ |
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if (index == ra->start && ra->size == ra->async_size) { |
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add_pages = get_next_ra_size(ra, max_pages); |
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if (ra->size + add_pages <= max_pages) { |
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ra->async_size = add_pages; |
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ra->size += add_pages; |
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} else { |
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ra->size = max_pages; |
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ra->async_size = max_pages >> 1; |
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} |
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} |
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|
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ractl->_index = ra->start; |
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do_page_cache_ra(ractl, ra->size, ra->async_size); |
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} |
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|
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void page_cache_sync_ra(struct readahead_control *ractl, |
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unsigned long req_count) |
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{ |
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bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM); |
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|
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/* |
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* Even if read-ahead is disabled, issue this request as read-ahead |
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* as we'll need it to satisfy the requested range. The forced |
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* read-ahead will do the right thing and limit the read to just the |
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* requested range, which we'll set to 1 page for this case. |
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*/ |
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if (!ractl->ra->ra_pages || blk_cgroup_congested()) { |
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if (!ractl->file) |
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return; |
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req_count = 1; |
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do_forced_ra = true; |
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} |
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|
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/* be dumb */ |
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if (do_forced_ra) { |
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force_page_cache_ra(ractl, req_count); |
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return; |
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} |
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|
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/* do read-ahead */ |
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ondemand_readahead(ractl, false, req_count); |
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} |
|
EXPORT_SYMBOL_GPL(page_cache_sync_ra); |
|
|
|
void page_cache_async_ra(struct readahead_control *ractl, |
|
struct page *page, unsigned long req_count) |
|
{ |
|
/* no read-ahead */ |
|
if (!ractl->ra->ra_pages) |
|
return; |
|
|
|
/* |
|
* Same bit is used for PG_readahead and PG_reclaim. |
|
*/ |
|
if (PageWriteback(page)) |
|
return; |
|
|
|
ClearPageReadahead(page); |
|
|
|
/* |
|
* Defer asynchronous read-ahead on IO congestion. |
|
*/ |
|
if (inode_read_congested(ractl->mapping->host)) |
|
return; |
|
|
|
if (blk_cgroup_congested()) |
|
return; |
|
|
|
/* do read-ahead */ |
|
ondemand_readahead(ractl, true, req_count); |
|
} |
|
EXPORT_SYMBOL_GPL(page_cache_async_ra); |
|
|
|
ssize_t ksys_readahead(int fd, loff_t offset, size_t count) |
|
{ |
|
ssize_t ret; |
|
struct fd f; |
|
|
|
ret = -EBADF; |
|
f = fdget(fd); |
|
if (!f.file || !(f.file->f_mode & FMODE_READ)) |
|
goto out; |
|
|
|
/* |
|
* The readahead() syscall is intended to run only on files |
|
* that can execute readahead. If readahead is not possible |
|
* on this file, then we must return -EINVAL. |
|
*/ |
|
ret = -EINVAL; |
|
if (!f.file->f_mapping || !f.file->f_mapping->a_ops || |
|
!S_ISREG(file_inode(f.file)->i_mode)) |
|
goto out; |
|
|
|
ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED); |
|
out: |
|
fdput(f); |
|
return ret; |
|
} |
|
|
|
SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count) |
|
{ |
|
return ksys_readahead(fd, offset, count); |
|
} |
|
|
|
/** |
|
* readahead_expand - Expand a readahead request |
|
* @ractl: The request to be expanded |
|
* @new_start: The revised start |
|
* @new_len: The revised size of the request |
|
* |
|
* Attempt to expand a readahead request outwards from the current size to the |
|
* specified size by inserting locked pages before and after the current window |
|
* to increase the size to the new window. This may involve the insertion of |
|
* THPs, in which case the window may get expanded even beyond what was |
|
* requested. |
|
* |
|
* The algorithm will stop if it encounters a conflicting page already in the |
|
* pagecache and leave a smaller expansion than requested. |
|
* |
|
* The caller must check for this by examining the revised @ractl object for a |
|
* different expansion than was requested. |
|
*/ |
|
void readahead_expand(struct readahead_control *ractl, |
|
loff_t new_start, size_t new_len) |
|
{ |
|
struct address_space *mapping = ractl->mapping; |
|
struct file_ra_state *ra = ractl->ra; |
|
pgoff_t new_index, new_nr_pages; |
|
gfp_t gfp_mask = readahead_gfp_mask(mapping); |
|
|
|
new_index = new_start / PAGE_SIZE; |
|
|
|
/* Expand the leading edge downwards */ |
|
while (ractl->_index > new_index) { |
|
unsigned long index = ractl->_index - 1; |
|
struct page *page = xa_load(&mapping->i_pages, index); |
|
|
|
if (page && !xa_is_value(page)) |
|
return; /* Page apparently present */ |
|
|
|
page = __page_cache_alloc(gfp_mask); |
|
if (!page) |
|
return; |
|
if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) { |
|
put_page(page); |
|
return; |
|
} |
|
|
|
ractl->_nr_pages++; |
|
ractl->_index = page->index; |
|
} |
|
|
|
new_len += new_start - readahead_pos(ractl); |
|
new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE); |
|
|
|
/* Expand the trailing edge upwards */ |
|
while (ractl->_nr_pages < new_nr_pages) { |
|
unsigned long index = ractl->_index + ractl->_nr_pages; |
|
struct page *page = xa_load(&mapping->i_pages, index); |
|
|
|
if (page && !xa_is_value(page)) |
|
return; /* Page apparently present */ |
|
|
|
page = __page_cache_alloc(gfp_mask); |
|
if (!page) |
|
return; |
|
if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) { |
|
put_page(page); |
|
return; |
|
} |
|
ractl->_nr_pages++; |
|
if (ra) { |
|
ra->size++; |
|
ra->async_size++; |
|
} |
|
} |
|
} |
|
EXPORT_SYMBOL(readahead_expand);
|
|
|