linux-stable/mm/readahead.c
Christoph Hellwig 176042404e mm: add PSI accounting around ->read_folio and ->readahead calls
PSI tries to account for the cost of bringing back in pages discarded by
the MM LRU management.  Currently the prime place for that is hooked into
the bio submission path, which is a rather bad place:

 - it does not actually account I/O for non-block file systems, of which
   we have many
 - it adds overhead and a layering violation to the block layer

Add the accounting into the two places in the core MM code that read
pages into an address space by calling into ->read_folio and ->readahead
so that the entire file system operations are covered, to broaden
the coverage and allow removing the accounting in the block layer going
forward.

As psi_memstall_enter can deal with nested calls this will not lead to
double accounting even while the bio annotations are still present.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20220915094200.139713-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-09-20 08:24:38 -06:00

850 lines
26 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* mm/readahead.c - address_space-level file readahead.
*
* Copyright (C) 2002, Linus Torvalds
*
* 09Apr2002 Andrew Morton
* Initial version.
*/
/**
* DOC: Readahead Overview
*
* Readahead is used to read content into the page cache before it is
* explicitly requested by the application. Readahead only ever
* attempts to read folios that are not yet in the page cache. If a
* folio is present but not up-to-date, readahead will not try to read
* it. In that case a simple ->read_folio() will be requested.
*
* Readahead is triggered when an application read request (whether a
* system call or a page fault) finds that the requested folio is not in
* the page cache, or that it is in the page cache and has the
* readahead flag set. This flag indicates that the folio was read
* as part of a previous readahead request and now that it has been
* accessed, it is time for the next readahead.
*
* Each readahead request is partly synchronous read, and partly async
* readahead. This is reflected in the struct file_ra_state which
* contains ->size being the total number of pages, and ->async_size
* which is the number of pages in the async section. The readahead
* flag will be set on the first folio in this async section to trigger
* a subsequent readahead. Once a series of sequential reads has been
* established, there should be no need for a synchronous component and
* all readahead request will be fully asynchronous.
*
* When either of the triggers causes a readahead, three numbers need
* to be determined: the start of the region to read, the size of the
* region, and the size of the async tail.
*
* The start of the region is simply the first page address at or after
* the accessed address, which is not currently populated in the page
* cache. This is found with a simple search in the page cache.
*
* The size of the async tail is determined by subtracting the size that
* was explicitly requested from the determined request size, unless
* this would be less than zero - then zero is used. NOTE THIS
* CALCULATION IS WRONG WHEN THE START OF THE REGION IS NOT THE ACCESSED
* PAGE. ALSO THIS CALCULATION IS NOT USED CONSISTENTLY.
*
* The size of the region is normally determined from the size of the
* previous readahead which loaded the preceding pages. This may be
* discovered from the struct file_ra_state for simple sequential reads,
* or from examining the state of the page cache when multiple
* sequential reads are interleaved. Specifically: where the readahead
* was triggered by the readahead flag, the size of the previous
* readahead is assumed to be the number of pages from the triggering
* page to the start of the new readahead. In these cases, the size of
* the previous readahead is scaled, often doubled, for the new
* readahead, though see get_next_ra_size() for details.
*
* If the size of the previous read cannot be determined, the number of
* preceding pages in the page cache is used to estimate the size of
* a previous read. This estimate could easily be misled by random
* reads being coincidentally adjacent, so it is ignored unless it is
* larger than the current request, and it is not scaled up, unless it
* is at the start of file.
*
* In general readahead is accelerated at the start of the file, as
* reads from there are often sequential. There are other minor
* adjustments to the readahead size in various special cases and these
* are best discovered by reading the code.
*
* The above calculation, based on the previous readahead size,
* determines the size of the readahead, to which any requested read
* size may be added.
*
* Readahead requests are sent to the filesystem using the ->readahead()
* address space operation, for which mpage_readahead() is a canonical
* implementation. ->readahead() should normally initiate reads on all
* folios, but may fail to read any or all folios without causing an I/O
* error. The page cache reading code will issue a ->read_folio() request
* for any folio which ->readahead() did not read, and only an error
* from this will be final.
*
* ->readahead() will generally call readahead_folio() repeatedly to get
* each folio from those prepared for readahead. It may fail to read a
* folio by:
*
* * not calling readahead_folio() sufficiently many times, effectively
* ignoring some folios, as might be appropriate if the path to
* storage is congested.
*
* * failing to actually submit a read request for a given folio,
* possibly due to insufficient resources, or
*
* * getting an error during subsequent processing of a request.
*
* In the last two cases, the folio should be unlocked by the filesystem
* to indicate that the read attempt has failed. In the first case the
* folio will be unlocked by the VFS.
*
* Those folios not in the final ``async_size`` of the request should be
* considered to be important and ->readahead() should not fail them due
* to congestion or temporary resource unavailability, but should wait
* for necessary resources (e.g. memory or indexing information) to
* become available. Folios in the final ``async_size`` may be
* considered less urgent and failure to read them is more acceptable.
* In this case it is best to use filemap_remove_folio() to remove the
* folios from the page cache as is automatically done for folios that
* were not fetched with readahead_folio(). This will allow a
* subsequent synchronous readahead request to try them again. If they
* are left in the page cache, then they will be read individually using
* ->read_folio() which may be less efficient.
*/
#include <linux/blkdev.h>
#include <linux/kernel.h>
#include <linux/dax.h>
#include <linux/gfp.h>
#include <linux/export.h>
#include <linux/backing-dev.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/pagevec.h>
#include <linux/pagemap.h>
#include <linux/psi.h>
#include <linux/syscalls.h>
#include <linux/file.h>
#include <linux/mm_inline.h>
#include <linux/blk-cgroup.h>
#include <linux/fadvise.h>
#include <linux/sched/mm.h>
#include "internal.h"
/*
* Initialise a struct file's readahead state. Assumes that the caller has
* memset *ra to zero.
*/
void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
{
ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
ra->prev_pos = -1;
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
static void read_pages(struct readahead_control *rac)
{
const struct address_space_operations *aops = rac->mapping->a_ops;
struct folio *folio;
struct blk_plug plug;
if (!readahead_count(rac))
return;
if (unlikely(rac->_workingset))
psi_memstall_enter(&rac->_pflags);
blk_start_plug(&plug);
if (aops->readahead) {
aops->readahead(rac);
/*
* Clean up the remaining folios. The sizes in ->ra
* may be used to size the next readahead, so make sure
* they accurately reflect what happened.
*/
while ((folio = readahead_folio(rac)) != NULL) {
unsigned long nr = folio_nr_pages(folio);
folio_get(folio);
rac->ra->size -= nr;
if (rac->ra->async_size >= nr) {
rac->ra->async_size -= nr;
filemap_remove_folio(folio);
}
folio_unlock(folio);
folio_put(folio);
}
} else {
while ((folio = readahead_folio(rac)) != NULL)
aops->read_folio(rac->file, folio);
}
blk_finish_plug(&plug);
if (unlikely(rac->_workingset))
psi_memstall_leave(&rac->_pflags);
rac->_workingset = false;
BUG_ON(readahead_count(rac));
}
/**
* page_cache_ra_unbounded - Start unchecked readahead.
* @ractl: Readahead control.
* @nr_to_read: The number of pages to read.
* @lookahead_size: Where to start the next readahead.
*
* This function is for filesystems to call when they want to start
* readahead beyond a file's stated i_size. This is almost certainly
* not the function you want to call. Use page_cache_async_readahead()
* or page_cache_sync_readahead() instead.
*
* Context: File is referenced by caller. Mutexes may be held by caller.
* May sleep, but will not reenter filesystem to reclaim memory.
*/
void page_cache_ra_unbounded(struct readahead_control *ractl,
unsigned long nr_to_read, unsigned long lookahead_size)
{
struct address_space *mapping = ractl->mapping;
unsigned long index = readahead_index(ractl);
gfp_t gfp_mask = readahead_gfp_mask(mapping);
unsigned long i;
/*
* Partway through the readahead operation, we will have added
* locked pages to the page cache, but will not yet have submitted
* them for I/O. Adding another page may need to allocate memory,
* which can trigger memory reclaim. Telling the VM we're in
* the middle of a filesystem operation will cause it to not
* touch file-backed pages, preventing a deadlock. Most (all?)
* filesystems already specify __GFP_NOFS in their mapping's
* gfp_mask, but let's be explicit here.
*/
unsigned int nofs = memalloc_nofs_save();
filemap_invalidate_lock_shared(mapping);
/*
* Preallocate as many pages as we will need.
*/
for (i = 0; i < nr_to_read; i++) {
struct folio *folio = xa_load(&mapping->i_pages, index + i);
if (folio && !xa_is_value(folio)) {
/*
* Page already present? Kick off the current batch
* of contiguous pages before continuing with the
* next batch. This page may be the one we would
* have intended to mark as Readahead, but we don't
* have a stable reference to this page, and it's
* not worth getting one just for that.
*/
read_pages(ractl);
ractl->_index++;
i = ractl->_index + ractl->_nr_pages - index - 1;
continue;
}
folio = filemap_alloc_folio(gfp_mask, 0);
if (!folio)
break;
if (filemap_add_folio(mapping, folio, index + i,
gfp_mask) < 0) {
folio_put(folio);
read_pages(ractl);
ractl->_index++;
i = ractl->_index + ractl->_nr_pages - index - 1;
continue;
}
if (i == nr_to_read - lookahead_size)
folio_set_readahead(folio);
ractl->_workingset |= folio_test_workingset(folio);
ractl->_nr_pages++;
}
/*
* Now start the IO. We ignore I/O errors - if the folio is not
* uptodate then the caller will launch read_folio again, and
* will then handle the error.
*/
read_pages(ractl);
filemap_invalidate_unlock_shared(mapping);
memalloc_nofs_restore(nofs);
}
EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
/*
* do_page_cache_ra() actually reads a chunk of disk. It allocates
* the pages first, then submits them for I/O. This avoids the very bad
* behaviour which would occur if page allocations are causing VM writeback.
* We really don't want to intermingle reads and writes like that.
*/
static void do_page_cache_ra(struct readahead_control *ractl,
unsigned long nr_to_read, unsigned long lookahead_size)
{
struct inode *inode = ractl->mapping->host;
unsigned long index = readahead_index(ractl);
loff_t isize = i_size_read(inode);
pgoff_t end_index; /* The last page we want to read */
if (isize == 0)
return;
end_index = (isize - 1) >> PAGE_SHIFT;
if (index > end_index)
return;
/* Don't read past the page containing the last byte of the file */
if (nr_to_read > end_index - index)
nr_to_read = end_index - index + 1;
page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size);
}
/*
* Chunk the readahead into 2 megabyte units, so that we don't pin too much
* memory at once.
*/
void force_page_cache_ra(struct readahead_control *ractl,
unsigned long nr_to_read)
{
struct address_space *mapping = ractl->mapping;
struct file_ra_state *ra = ractl->ra;
struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
unsigned long max_pages, index;
if (unlikely(!mapping->a_ops->read_folio && !mapping->a_ops->readahead))
return;
/*
* If the request exceeds the readahead window, allow the read to
* be up to the optimal hardware IO size
*/
index = readahead_index(ractl);
max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
while (nr_to_read) {
unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
ractl->_index = index;
do_page_cache_ra(ractl, this_chunk, 0);
index += this_chunk;
nr_to_read -= this_chunk;
}
}
/*
* Set the initial window size, round to next power of 2 and square
* for small size, x 4 for medium, and x 2 for large
* for 128k (32 page) max ra
* 1-2 page = 16k, 3-4 page 32k, 5-8 page = 64k, > 8 page = 128k initial
*/
static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
{
unsigned long newsize = roundup_pow_of_two(size);
if (newsize <= max / 32)
newsize = newsize * 4;
else if (newsize <= max / 4)
newsize = newsize * 2;
else
newsize = max;
return newsize;
}
/*
* Get the previous window size, ramp it up, and
* return it as the new window size.
*/
static unsigned long get_next_ra_size(struct file_ra_state *ra,
unsigned long max)
{
unsigned long cur = ra->size;
if (cur < max / 16)
return 4 * cur;
if (cur <= max / 2)
return 2 * cur;
return max;
}
/*
* On-demand readahead design.
*
* The fields in struct file_ra_state represent the most-recently-executed
* readahead attempt:
*
* |<----- async_size ---------|
* |------------------- size -------------------->|
* |==================#===========================|
* ^start ^page marked with PG_readahead
*
* To overlap application thinking time and disk I/O time, we do
* `readahead pipelining': Do not wait until the application consumed all
* readahead pages and stalled on the missing page at readahead_index;
* Instead, submit an asynchronous readahead I/O as soon as there are
* only async_size pages left in the readahead window. Normally async_size
* will be equal to size, for maximum pipelining.
*
* In interleaved sequential reads, concurrent streams on the same fd can
* be invalidating each other's readahead state. So we flag the new readahead
* page at (start+size-async_size) with PG_readahead, and use it as readahead
* indicator. The flag won't be set on already cached pages, to avoid the
* readahead-for-nothing fuss, saving pointless page cache lookups.
*
* prev_pos tracks the last visited byte in the _previous_ read request.
* It should be maintained by the caller, and will be used for detecting
* small random reads. Note that the readahead algorithm checks loosely
* for sequential patterns. Hence interleaved reads might be served as
* sequential ones.
*
* There is a special-case: if the first page which the application tries to
* read happens to be the first page of the file, it is assumed that a linear
* read is about to happen and the window is immediately set to the initial size
* based on I/O request size and the max_readahead.
*
* The code ramps up the readahead size aggressively at first, but slow down as
* it approaches max_readhead.
*/
/*
* Count contiguously cached pages from @index-1 to @index-@max,
* this count is a conservative estimation of
* - length of the sequential read sequence, or
* - thrashing threshold in memory tight systems
*/
static pgoff_t count_history_pages(struct address_space *mapping,
pgoff_t index, unsigned long max)
{
pgoff_t head;
rcu_read_lock();
head = page_cache_prev_miss(mapping, index - 1, max);
rcu_read_unlock();
return index - 1 - head;
}
/*
* page cache context based readahead
*/
static int try_context_readahead(struct address_space *mapping,
struct file_ra_state *ra,
pgoff_t index,
unsigned long req_size,
unsigned long max)
{
pgoff_t size;
size = count_history_pages(mapping, index, max);
/*
* not enough history pages:
* it could be a random read
*/
if (size <= req_size)
return 0;
/*
* starts from beginning of file:
* it is a strong indication of long-run stream (or whole-file-read)
*/
if (size >= index)
size *= 2;
ra->start = index;
ra->size = min(size + req_size, max);
ra->async_size = 1;
return 1;
}
/*
* There are some parts of the kernel which assume that PMD entries
* are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then,
* limit the maximum allocation order to PMD size. I'm not aware of any
* assumptions about maximum order if THP are disabled, but 8 seems like
* a good order (that's 1MB if you're using 4kB pages)
*/
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER
#else
#define MAX_PAGECACHE_ORDER 8
#endif
static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
pgoff_t mark, unsigned int order, gfp_t gfp)
{
int err;
struct folio *folio = filemap_alloc_folio(gfp, order);
if (!folio)
return -ENOMEM;
mark = round_up(mark, 1UL << order);
if (index == mark)
folio_set_readahead(folio);
err = filemap_add_folio(ractl->mapping, folio, index, gfp);
if (err) {
folio_put(folio);
return err;
}
ractl->_nr_pages += 1UL << order;
ractl->_workingset |= folio_test_workingset(folio);
return 0;
}
void page_cache_ra_order(struct readahead_control *ractl,
struct file_ra_state *ra, unsigned int new_order)
{
struct address_space *mapping = ractl->mapping;
pgoff_t index = readahead_index(ractl);
pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
pgoff_t mark = index + ra->size - ra->async_size;
int err = 0;
gfp_t gfp = readahead_gfp_mask(mapping);
if (!mapping_large_folio_support(mapping) || ra->size < 4)
goto fallback;
limit = min(limit, index + ra->size - 1);
if (new_order < MAX_PAGECACHE_ORDER) {
new_order += 2;
if (new_order > MAX_PAGECACHE_ORDER)
new_order = MAX_PAGECACHE_ORDER;
while ((1 << new_order) > ra->size)
new_order--;
}
filemap_invalidate_lock_shared(mapping);
while (index <= limit) {
unsigned int order = new_order;
/* Align with smaller pages if needed */
if (index & ((1UL << order) - 1)) {
order = __ffs(index);
if (order == 1)
order = 0;
}
/* Don't allocate pages past EOF */
while (index + (1UL << order) - 1 > limit) {
if (--order == 1)
order = 0;
}
err = ra_alloc_folio(ractl, index, mark, order, gfp);
if (err)
break;
index += 1UL << order;
}
if (index > limit) {
ra->size += index - limit - 1;
ra->async_size += index - limit - 1;
}
read_pages(ractl);
filemap_invalidate_unlock_shared(mapping);
/*
* If there were already pages in the page cache, then we may have
* left some gaps. Let the regular readahead code take care of this
* situation.
*/
if (!err)
return;
fallback:
do_page_cache_ra(ractl, ra->size, ra->async_size);
}
/*
* A minimal readahead algorithm for trivial sequential/random reads.
*/
static void ondemand_readahead(struct readahead_control *ractl,
struct folio *folio, unsigned long req_size)
{
struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
struct file_ra_state *ra = ractl->ra;
unsigned long max_pages = ra->ra_pages;
unsigned long add_pages;
pgoff_t index = readahead_index(ractl);
pgoff_t expected, prev_index;
unsigned int order = folio ? folio_order(folio) : 0;
/*
* If the request exceeds the readahead window, allow the read to
* be up to the optimal hardware IO size
*/
if (req_size > max_pages && bdi->io_pages > max_pages)
max_pages = min(req_size, bdi->io_pages);
/*
* start of file
*/
if (!index)
goto initial_readahead;
/*
* It's the expected callback index, assume sequential access.
* Ramp up sizes, and push forward the readahead window.
*/
expected = round_up(ra->start + ra->size - ra->async_size,
1UL << order);
if (index == expected || index == (ra->start + ra->size)) {
ra->start += ra->size;
ra->size = get_next_ra_size(ra, max_pages);
ra->async_size = ra->size;
goto readit;
}
/*
* Hit a marked folio without valid readahead state.
* E.g. interleaved reads.
* Query the pagecache for async_size, which normally equals to
* readahead size. Ramp it up and use it as the new readahead size.
*/
if (folio) {
pgoff_t start;
rcu_read_lock();
start = page_cache_next_miss(ractl->mapping, index + 1,
max_pages);
rcu_read_unlock();
if (!start || start - index > max_pages)
return;
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(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;
page_cache_ra_order(ractl, ra, order);
}
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 readahead is disabled, issue this request as readahead
* as we'll need it to satisfy the requested range. The forced
* readahead 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;
}
ondemand_readahead(ractl, NULL, 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 readahead */
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);
if (blk_cgroup_congested())
return;
ondemand_readahead(ractl, folio, 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);
}
#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_READAHEAD)
COMPAT_SYSCALL_DEFINE4(readahead, int, fd, compat_arg_u64_dual(offset), size_t, count)
{
return ksys_readahead(fd, compat_arg_u64_glue(offset), count);
}
#endif
/**
* 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;
}
if (unlikely(PageWorkingset(page)) && !ractl->_workingset) {
ractl->_workingset = true;
psi_memstall_enter(&ractl->_pflags);
}
ractl->_nr_pages++;
if (ra) {
ra->size++;
ra->async_size++;
}
}
}
EXPORT_SYMBOL(readahead_expand);