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![Matthew Wilcox (Oracle)](/assets/img/avatar_default.png)
This saves 99 bytes of kernel text. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
716 lines
20 KiB
C
716 lines
20 KiB
C
// 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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#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/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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#include "internal.h"
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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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* 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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* 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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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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* 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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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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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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EXPORT_SYMBOL(read_cache_pages);
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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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if (!readahead_count(rac))
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goto out;
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blk_start_plug(&plug);
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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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* 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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* 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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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 folio *folio = xa_load(&mapping->i_pages, index + i);
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if (folio && !xa_is_value(folio)) {
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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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folio = filemap_alloc_folio(gfp_mask, 0);
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if (!folio)
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break;
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if (mapping->a_ops->readpages) {
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folio->index = index + i;
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list_add(&folio->lru, &page_pool);
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} else if (filemap_add_folio(mapping, folio, index + i,
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gfp_mask) < 0) {
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folio_put(folio);
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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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folio_set_readahead(folio);
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ractl->_nr_pages++;
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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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* 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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* 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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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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* 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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* 1-2 page = 16k, 3-4 page 32k, 5-8 page = 64k, > 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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* 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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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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* 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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* 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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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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return index - 1 - head;
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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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* 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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* 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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* 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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* 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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* 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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* 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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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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if (!start || start - index > max_pages)
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return;
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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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* 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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* 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)
|
|
goto initial_readahead;
|
|
|
|
/*
|
|
* Query the page cache and look for the traces(cached history pages)
|
|
* that a sequential stream would leave behind.
|
|
*/
|
|
if (try_context_readahead(ractl->mapping, ra, index, req_size,
|
|
max_pages))
|
|
goto readit;
|
|
|
|
/*
|
|
* standalone, small random read
|
|
* Read as is, and do not pollute the readahead state.
|
|
*/
|
|
do_page_cache_ra(ractl, req_size, 0);
|
|
return;
|
|
|
|
initial_readahead:
|
|
ra->start = index;
|
|
ra->size = get_init_ra_size(req_size, max_pages);
|
|
ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
|
|
|
|
readit:
|
|
/*
|
|
* Will this read hit the readahead marker made by itself?
|
|
* If so, trigger the readahead marker hit now, and merge
|
|
* the resulted next readahead window into the current one.
|
|
* Take care of maximum IO pages as above.
|
|
*/
|
|
if (index == ra->start && ra->size == ra->async_size) {
|
|
add_pages = get_next_ra_size(ra, max_pages);
|
|
if (ra->size + add_pages <= max_pages) {
|
|
ra->async_size = add_pages;
|
|
ra->size += add_pages;
|
|
} else {
|
|
ra->size = max_pages;
|
|
ra->async_size = max_pages >> 1;
|
|
}
|
|
}
|
|
|
|
ractl->_index = ra->start;
|
|
do_page_cache_ra(ractl, ra->size, ra->async_size);
|
|
}
|
|
|
|
void page_cache_sync_ra(struct readahead_control *ractl,
|
|
unsigned long req_count)
|
|
{
|
|
bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
|
|
|
|
/*
|
|
* Even if read-ahead is disabled, issue this request as read-ahead
|
|
* as we'll need it to satisfy the requested range. The forced
|
|
* read-ahead will do the right thing and limit the read to just the
|
|
* requested range, which we'll set to 1 page for this case.
|
|
*/
|
|
if (!ractl->ra->ra_pages || blk_cgroup_congested()) {
|
|
if (!ractl->file)
|
|
return;
|
|
req_count = 1;
|
|
do_forced_ra = true;
|
|
}
|
|
|
|
/* be dumb */
|
|
if (do_forced_ra) {
|
|
force_page_cache_ra(ractl, req_count);
|
|
return;
|
|
}
|
|
|
|
/* do read-ahead */
|
|
ondemand_readahead(ractl, false, req_count);
|
|
}
|
|
EXPORT_SYMBOL_GPL(page_cache_sync_ra);
|
|
|
|
void page_cache_async_ra(struct readahead_control *ractl,
|
|
struct folio *folio, unsigned long req_count)
|
|
{
|
|
/* no read-ahead */
|
|
if (!ractl->ra->ra_pages)
|
|
return;
|
|
|
|
/*
|
|
* Same bit is used for PG_readahead and PG_reclaim.
|
|
*/
|
|
if (folio_test_writeback(folio))
|
|
return;
|
|
|
|
folio_clear_readahead(folio);
|
|
|
|
/*
|
|
* 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);
|