linux.git/mm/readahead.c, branch v5.14

mm: Implement readahead_control pageset expansion

2021-04-23T09:14:29+00:00

Provide a function, readahead_expand(), that expands the set of pages
specified by a readahead_control object to encompass a revised area with a
proposed size and length.

The proposed area must include all of the old area and may be expanded yet
more by this function so that the edges align on (transparent huge) page
boundaries as allocated.

The expansion will be cut short if a page already exists in either of the
areas being expanded into.  Note that any expansion made in such a case is
not rolled back.

This will be used by fscache so that reads can be expanded to cache granule
boundaries, thereby allowing whole granules to be stored in the cache, but
there are other potential users also.

Changes:
v6:
- Fold in a patch from Matthew Wilcox to tell the ondemand readahead
  algorithm about the expansion so that the next readahead starts at the
  right place[2].

v4:
- Moved the declaration of readahead_expand() to a better place[1].

Suggested-by: Matthew Wilcox (Oracle) 
Signed-off-by: David Howells 
Reviewed-by: Matthew Wilcox (Oracle) 
Tested-by: Jeff Layton 
Tested-by: Dave Wysochanski 
Tested-By: Marc Dionne 
cc: Alexander Viro 
cc: Christoph Hellwig 
cc: Mike Marshall 
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20210217161358.GM2858050@casper.infradead.org/ [1]
Link: https://lore.kernel.org/r/20210407201857.3582797-4-willy@infradead.org/ [2]
Link: https://lore.kernel.org/r/159974633888.2094769.8326206446358128373.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/160588479816.3465195.553952688795241765.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118131787.1232039.4863969952441067985.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161028670.2537118.13831420617039766044.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340389201.1303470.14353807284546854878.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539530488.286939.18085961677838089157.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653789422.2770958.2108046612147345000.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789069829.6155.4295672417565512161.stgit@warthog.procyon.org.uk/ # v6

mm/readahead: Handle ractl nr_pages being modified

2021-04-23T09:14:28+00:00

Filesystems are not currently permitted to modify the number of pages
in the ractl.  An upcoming patch to add readahead_expand() changes that
rule, so remove the check and resync the loop counter after every call
to the filesystem.

Tested-by: Jeff Layton 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20210420200116.3715790-1-willy@infradead.org/
Link: https://lore.kernel.org/r/20210421170923.4005574-1-willy@infradead.org/ # v2

mm/filemap: Pass the file_ra_state in the ractl

2021-04-23T08:25:00+00:00

For readahead_expand(), we need to modify the file ra_state, so pass it
down by adding it to the ractl.  We have to do this because it's not always
the same as f_ra in the struct file that is already being passed.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: David Howells 
Tested-by: Jeff Layton 
Tested-by: Dave Wysochanski 
Tested-By: Marc Dionne 
Link: https://lore.kernel.org/r/20210407201857.3582797-2-willy@infradead.org/
Link: https://lore.kernel.org/r/161789067431.6155.8063840447229665720.stgit@warthog.procyon.org.uk/ # v6

mm: use limited read-ahead to satisfy read

2020-10-17T19:49:08+00:00

For the case where read-ahead is disabled on the file, or if the cgroup
is congested, ensure that we can at least do 1 page of read-ahead to
make progress on the read in an async fashion. This could potentially be
larger, but it's not needed in terms of functionality, so let's error on
the side of caution as larger counts of pages may run into reclaim
issues (particularly if we're congested).

This makes sure we're not hitting the potentially sync ->readpage() path
for IO that is marked IOCB_WAITQ, which could cause us to block. It also
means we'll use the same path for IO, regardless of whether or not
read-ahead happens to be disabled on the lower level device.

Acked-by: Johannes Weiner 
Reported-by: Matthew Wilcox (Oracle) 
Reported-by: Hao_Xu 
[axboe: updated for new ractl API]
Signed-off-by: Jens Axboe

mm/readahead: pass a file_ra_state into force_page_cache_ra

2020-10-16T18:11:16+00:00

The file_ra_state being passed into page_cache_sync_readahead() was being
ignored in favour of using the one embedded in the struct file.  The only
caller for which this makes a difference is the fsverity code if the file
has been marked as POSIX_FADV_RANDOM, but it's confusing and worth fixing.

Signed-off-by: David Howells 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-10-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/readahead: add page_cache_sync_ra and page_cache_async_ra

2020-10-16T18:11:16+00:00

Reimplement page_cache_sync_readahead() and page_cache_async_readahead()
as wrappers around versions of the function which take a readahead_control
in preparation for making do_sync_mmap_readahead() pass down an RAC
struct.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: David Howells 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-8-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/readahead: pass readahead_control to force_page_cache_ra

2020-10-16T18:11:16+00:00

Reimplement force_page_cache_readahead() as a wrapper around
force_page_cache_ra().  Pass the existing readahead_control from
page_cache_sync_readahead().

Signed-off-by: David Howells 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-7-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/readahead: make ondemand_readahead take a readahead_control

2020-10-16T18:11:16+00:00

Make ondemand_readahead() take a readahead_control struct in preparation
for making do_sync_mmap_readahead() pass down an RAC struct.

Signed-off-by: David Howells 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-6-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/readahead: make do_page_cache_ra take a readahead_control

2020-10-16T18:11:16+00:00

Rename __do_page_cache_readahead() to do_page_cache_ra() and call it
directly from ondemand_readahead() instead of indirecting via ra_submit().

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: David Howells 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-5-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/readahead: make page_cache_ra_unbounded take a readahead_control

2020-10-16T18:11:16+00:00

Define it in the callers instead of in page_cache_ra_unbounded().

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Cc: David Howells 
Cc: Eric Biggers 
Link: https://lkml.kernel.org/r/20200903140844.14194-4-willy@infradead.org
Signed-off-by: Linus Torvalds