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readahead: disentangle async and sync readahead

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Both async and sync readahead are handled by ondemand_readahead()
function.  However there isn't actually much in common.  Just move async
related parts into page_cache_ra_async() and sync related parts to
page_cache_ra_sync().  No functional changes.

Link: https://lkml.kernel.org/r/20240625101909.12234-8-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Tested-by: Zhang Peng <zhangpengpeng0808@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jan Kara 2024-06-25 12:18:58 +02:00 committed by Andrew Morton
parent 0b1efc3e78
commit 3a7a11a57e
1 changed files with 79 additions and 87 deletions
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166
mm/readahead.c
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@ -540,18 +540,11 @@ void page_cache_ra_order(struct readahead_control *ractl,
do_page_cache_ra(ractl, ra->size - (index - start), 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)
static unsigned long ractl_max_pages(struct readahead_control *ractl,
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;
pgoff_t index = readahead_index(ractl);
pgoff_t expected, prev_index;
unsigned int order = folio ? folio_order(folio) : 0;
unsigned long max_pages = ractl->ra->ra_pages;
/*
* If the request exceeds the readahead window, allow the read to
@ -559,55 +552,42 @@ static void ondemand_readahead(struct readahead_control *ractl,
*/
if (req_size > max_pages && bdi->io_pages > max_pages)
max_pages = min(req_size, bdi->io_pages);
return max_pages;
}
void page_cache_sync_ra(struct readahead_control *ractl,
unsigned long req_count)
{
pgoff_t index = readahead_index(ractl);
bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
struct file_ra_state *ra = ractl->ra;
unsigned long max_pages;
pgoff_t prev_index;
/*
* start of file
* 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 (!index)
goto initial_readahead;
/*
* It's the expected callback index, assume sequential access.
* Ramp up sizes, and push forward the readahead window.
*/
expected = round_down(ra->start + ra->size - ra->async_size,
1UL << order);
if (folio && index == expected) {
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)
if (!ra->ra_pages || blk_cgroup_congested()) {
if (!ractl->file)
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;
req_count = 1;
do_forced_ra = true;
}
/* be dumb */
if (do_forced_ra) {
force_page_cache_ra(ractl, req_count);
return;
}
max_pages = ractl_max_pages(ractl, req_count);
/*
* oversize read
* start of file or oversized read
*/
if (req_size > max_pages)
if (!index || req_count > max_pages)
goto initial_readahead;
/*
@ -623,7 +603,7 @@ static void ondemand_readahead(struct readahead_control *ractl,
* 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,
if (try_context_readahead(ractl->mapping, ra, index, req_count,
max_pages))
goto readit;
@ -631,53 +611,31 @@ static void ondemand_readahead(struct readahead_control *ractl,
* standalone, small random read
* Read as is, and do not pollute the readahead state.
*/
do_page_cache_ra(ractl, req_size, 0);
do_page_cache_ra(ractl, req_count, 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 >> 1;
ra->size = get_init_ra_size(req_count, max_pages);
ra->async_size = ra->size > req_count ? ra->size - req_count :
ra->size >> 1;
readit:
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);
page_cache_ra_order(ractl, ra, 0);
}
EXPORT_SYMBOL_GPL(page_cache_sync_ra);
void page_cache_async_ra(struct readahead_control *ractl,
struct folio *folio, unsigned long req_count)
{
unsigned long max_pages;
struct file_ra_state *ra = ractl->ra;
pgoff_t index = readahead_index(ractl);
pgoff_t expected, start;
unsigned int order = folio_order(folio);
/* no readahead */
if (!ractl->ra->ra_pages)
if (!ra->ra_pages)
return;
/*
@ -691,7 +649,41 @@ void page_cache_async_ra(struct readahead_control *ractl,
if (blk_cgroup_congested())
return;
ondemand_readahead(ractl, folio, req_count);
max_pages = ractl_max_pages(ractl, req_count);
/*
* It's the expected callback index, assume sequential access.
* Ramp up sizes, and push forward the readahead window.
*/
expected = round_down(ra->start + ra->size - ra->async_size,
1UL << order);
if (index == expected) {
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.
*/
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_count;
ra->size = get_next_ra_size(ra, max_pages);
ra->async_size = ra->size;
readit:
ractl->_index = ra->start;
page_cache_ra_order(ractl, ra, order);
}
EXPORT_SYMBOL_GPL(page_cache_async_ra);