![Matthew Wilcox (Oracle)](/assets/img/avatar_default.png)
Patch series "Readahead patches for 5.9/5.10".
These are infrastructure for both the THP patchset and for the fscache
rewrite,
For both pieces of infrastructure being build on top of this patchset, we
want the ractl to be available higher in the call-stack.
For David's work, he wants to add the 'critical page' to the ractl so that
he knows which page NEEDS to be brought in from storage, and which ones
are nice-to-have. We might want something similar in block storage too.
It used to be simple -- the first page was the critical one, but then mmap
added fault-around and so for that usecase, the middle page is the
critical one. Anyway, I don't have any code to show that yet, we just
know that the lowest point in the callchain where we have that information
is do_sync_mmap_readahead() and so the ractl needs to start its life
there.
For THP, we havew the code that needs it. It's actually the apex patch to
the series; the one which finally starts to allocate THPs and present them
to consenting filesystems:
798bcf30ab
This patch (of 8):
Allow for a more concise definition of a struct readahead_control.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Biggers <ebiggers@google.com>
Cc: David Howells <dhowells@redhat.com>
Link: https://lkml.kernel.org/r/20200903140844.14194-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20200903140844.14194-3-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
661 lines
18 KiB
C
661 lines
18 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/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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#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_readahead_unbounded - Start unchecked readahead.
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* @mapping: File address space.
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* @file: This instance of the open file; used for authentication.
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* @index: First page index to read.
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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_readahead_unbounded(struct address_space *mapping,
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struct file *file, pgoff_t index, unsigned long nr_to_read,
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unsigned long lookahead_size)
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{
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LIST_HEAD(page_pool);
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gfp_t gfp_mask = readahead_gfp_mask(mapping);
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DEFINE_READAHEAD(rac, file, mapping, index);
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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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/*
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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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BUG_ON(index + i != rac._index + rac._nr_pages);
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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(&rac, &page_pool, true);
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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(&rac, &page_pool, true);
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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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rac._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(&rac, &page_pool, false);
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memalloc_nofs_restore(nofs);
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}
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EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);
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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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void __do_page_cache_readahead(struct address_space *mapping,
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struct file *file, pgoff_t index, 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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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_readahead_unbounded(mapping, file, index, nr_to_read,
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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_readahead(struct address_space *mapping,
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struct file *filp, pgoff_t index, 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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!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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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, index, 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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* 1-8 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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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 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 index,
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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_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(mapping, index + 1, 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;
|
|
ra->size = start - index; /* old async_size */
|
|
ra->size += req_size;
|
|
ra->size = get_next_ra_size(ra, max_pages);
|
|
ra->async_size = ra->size;
|
|
goto readit;
|
|
}
|
|
|
|
/*
|
|
* oversize read
|
|
*/
|
|
if (req_size > max_pages)
|
|
goto initial_readahead;
|
|
|
|
/*
|
|
* sequential cache miss
|
|
* trivial case: (index - prev_index) == 1
|
|
* unaligned reads: (index - prev_index) == 0
|
|
*/
|
|
prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
|
|
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(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_readahead(mapping, filp, index, 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;
|
|
}
|
|
}
|
|
|
|
ra_submit(ra, mapping, filp);
|
|
}
|
|
|
|
/**
|
|
* page_cache_sync_readahead - generic file readahead
|
|
* @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()
|
|
* @index: Index of first page to be read.
|
|
* @req_count: Total number of pages being read by the caller.
|
|
*
|
|
* page_cache_sync_readahead() should be called when a cache miss happened:
|
|
* it will submit the read. The readahead logic may decide to piggyback more
|
|
* 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 index, unsigned long req_count)
|
|
{
|
|
/* 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, index, req_count);
|
|
return;
|
|
}
|
|
|
|
/* do read-ahead */
|
|
ondemand_readahead(mapping, ra, filp, false, index, req_count);
|
|
}
|
|
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 @index which triggered the readahead call.
|
|
* @index: Index of first page to be read.
|
|
* @req_count: Total number of pages being read by the caller.
|
|
*
|
|
* page_cache_async_readahead() should be called when a page is used which
|
|
* is marked as PageReadahead; 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 index,
|
|
unsigned long req_count)
|
|
{
|
|
/* 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, index, req_count);
|
|
}
|
|
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);
|
|
}
|