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3d8f761531
The implementation of readahead(2) syscall is identical to that of
fadvise64(POSIX_FADV_WILLNEED) with a few exceptions:
1. readahead(2) returns -EINVAL for !mapping->a_ops and fadvise64()
ignores the request and returns 0.
2. fadvise64() checks for integer overflow corner case
3. fadvise64() calls the optional filesystem fadvise() file operation
Unite the two implementations by calling vfs_fadvise() from readahead(2)
syscall. Check the !mapping->a_ops in readahead(2) syscall to preserve
documented syscall ABI behaviour.
Suggested-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: d1d04ef857
("ovl: stack file ops")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
609 lines
16 KiB
C
609 lines
16 KiB
C
/*
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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/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 "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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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 int read_pages(struct address_space *mapping, struct file *filp,
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struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
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{
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struct blk_plug plug;
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unsigned page_idx;
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int ret;
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blk_start_plug(&plug);
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if (mapping->a_ops->readpages) {
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ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
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/* Clean up the remaining pages */
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put_pages_list(pages);
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goto out;
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}
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for (page_idx = 0; page_idx < nr_pages; page_idx++) {
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struct page *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, gfp))
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mapping->a_ops->readpage(filp, page);
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put_page(page);
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}
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ret = 0;
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out:
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blk_finish_plug(&plug);
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return ret;
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}
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/*
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* __do_page_cache_readahead() 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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* Returns the number of pages requested, or the maximum amount of I/O allowed.
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*/
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unsigned int __do_page_cache_readahead(struct address_space *mapping,
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struct file *filp, pgoff_t offset, unsigned long nr_to_read,
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unsigned long lookahead_size)
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{
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struct inode *inode = mapping->host;
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struct page *page;
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unsigned long end_index; /* The last page we want to read */
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LIST_HEAD(page_pool);
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int page_idx;
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unsigned int nr_pages = 0;
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loff_t isize = i_size_read(inode);
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gfp_t gfp_mask = readahead_gfp_mask(mapping);
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if (isize == 0)
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goto out;
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end_index = ((isize - 1) >> PAGE_SHIFT);
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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 (page_idx = 0; page_idx < nr_to_read; page_idx++) {
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pgoff_t page_offset = offset + page_idx;
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if (page_offset > end_index)
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break;
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rcu_read_lock();
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page = radix_tree_lookup(&mapping->i_pages, page_offset);
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rcu_read_unlock();
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if (page && !radix_tree_exceptional_entry(page)) {
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/*
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* Page already present? Kick off the current batch of
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* contiguous pages before continuing with the next
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* batch.
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*/
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if (nr_pages)
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read_pages(mapping, filp, &page_pool, nr_pages,
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gfp_mask);
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nr_pages = 0;
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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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page->index = page_offset;
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list_add(&page->lru, &page_pool);
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if (page_idx == nr_to_read - lookahead_size)
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SetPageReadahead(page);
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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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if (nr_pages)
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read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
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BUG_ON(!list_empty(&page_pool));
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out:
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return nr_pages;
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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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int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
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pgoff_t offset, unsigned long nr_to_read)
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{
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struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
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struct file_ra_state *ra = &filp->f_ra;
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unsigned long max_pages;
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if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
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return -EINVAL;
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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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max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
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nr_to_read = min(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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__do_page_cache_readahead(mapping, filp, offset, this_chunk, 0);
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offset += this_chunk;
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nr_to_read -= this_chunk;
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}
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return 0;
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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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* 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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unsigned long newsize;
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if (cur < max / 16)
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newsize = 4 * cur;
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else
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newsize = 2 * cur;
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return min(newsize, 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 @offset-1 to @offset-@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 offset, 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_hole(mapping, offset - 1, max);
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rcu_read_unlock();
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return offset - 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 offset,
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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, offset, 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 >= offset)
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size *= 2;
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ra->start = offset;
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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 unsigned long
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ondemand_readahead(struct address_space *mapping,
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struct file_ra_state *ra, struct file *filp,
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bool hit_readahead_marker, pgoff_t offset,
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unsigned long req_size)
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{
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struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
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unsigned long max_pages = ra->ra_pages;
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unsigned long add_pages;
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pgoff_t prev_offset;
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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 (!offset)
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goto initial_readahead;
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/*
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* It's the expected callback offset, 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 ((offset == (ra->start + ra->size - ra->async_size) ||
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offset == (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_hole(mapping, offset + 1, max_pages);
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rcu_read_unlock();
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if (!start || start - offset > max_pages)
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return 0;
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ra->start = start;
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ra->size = start - offset; /* 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: (offset - prev_offset) == 1
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* unaligned reads: (offset - prev_offset) == 0
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*/
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prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
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if (offset - prev_offset <= 1UL)
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goto initial_readahead;
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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(mapping, ra, offset, req_size, max_pages))
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goto readit;
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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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return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
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initial_readahead:
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ra->start = offset;
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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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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 (offset == 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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return ra_submit(ra, mapping, filp);
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}
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/**
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* page_cache_sync_readahead - generic file readahead
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* @mapping: address_space which holds the pagecache and I/O vectors
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* @ra: file_ra_state which holds the readahead state
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* @filp: passed on to ->readpage() and ->readpages()
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* @offset: start offset into @mapping, in pagecache page-sized units
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* @req_size: hint: total size of the read which the caller is performing in
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* pagecache pages
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*
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* page_cache_sync_readahead() should be called when a cache miss happened:
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* it will submit the read. The readahead logic may decide to piggyback more
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* pages onto the read request if access patterns suggest it will improve
|
|
* performance.
|
|
*/
|
|
void page_cache_sync_readahead(struct address_space *mapping,
|
|
struct file_ra_state *ra, struct file *filp,
|
|
pgoff_t offset, unsigned long req_size)
|
|
{
|
|
/* no read-ahead */
|
|
if (!ra->ra_pages)
|
|
return;
|
|
|
|
if (blk_cgroup_congested())
|
|
return;
|
|
|
|
/* be dumb */
|
|
if (filp && (filp->f_mode & FMODE_RANDOM)) {
|
|
force_page_cache_readahead(mapping, filp, offset, req_size);
|
|
return;
|
|
}
|
|
|
|
/* do read-ahead */
|
|
ondemand_readahead(mapping, ra, filp, false, offset, req_size);
|
|
}
|
|
EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
|
|
|
|
/**
|
|
* page_cache_async_readahead - file readahead for marked pages
|
|
* @mapping: address_space which holds the pagecache and I/O vectors
|
|
* @ra: file_ra_state which holds the readahead state
|
|
* @filp: passed on to ->readpage() and ->readpages()
|
|
* @page: the page at @offset which has the PG_readahead flag set
|
|
* @offset: start offset into @mapping, in pagecache page-sized units
|
|
* @req_size: hint: total size of the read which the caller is performing in
|
|
* pagecache pages
|
|
*
|
|
* page_cache_async_readahead() should be called when a page is used which
|
|
* has the PG_readahead flag; this is a marker to suggest that the application
|
|
* has used up enough of the readahead window that we should start pulling in
|
|
* more pages.
|
|
*/
|
|
void
|
|
page_cache_async_readahead(struct address_space *mapping,
|
|
struct file_ra_state *ra, struct file *filp,
|
|
struct page *page, pgoff_t offset,
|
|
unsigned long req_size)
|
|
{
|
|
/* no read-ahead */
|
|
if (!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(mapping->host))
|
|
return;
|
|
|
|
if (blk_cgroup_congested())
|
|
return;
|
|
|
|
/* do read-ahead */
|
|
ondemand_readahead(mapping, ra, filp, true, offset, req_size);
|
|
}
|
|
EXPORT_SYMBOL_GPL(page_cache_async_readahead);
|
|
|
|
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);
|
|
}
|