Commit 6ac40147 authored by Jan Kara's avatar Jan Kara Committed by Tong Tiangen
Browse files

readahead: don't shorten readahead window in read_pages() 

mainline inclusion
from mainline-v6.14-rc1
commit 7a1eb89f79188ec32599064eca7c14d42260760a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IBRWBB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7a1eb89f79188ec32599064eca7c14d42260760a

--------------------------------

Patch series "readahead: Reintroduce fix for improper RA window sizing".

This small patch series reintroduces a fix of readahead window confusion
(and thus read throughput reduction) when page_cache_ra_order() ends up
failing due to folios already present in the page cache.  After thinking
about this for a while I have ended up with a dumb fix that just rechecks
if we have something to read before calling do_page_cache_ra().  This
fixes the problem reported in [1].  I still think it doesn't make much
sense to update readahead window size in read_pages() so patch 1 removes
that but the real fix in patch 2 does not depend on it.

[1] https://lore.kernel.org/all/49648605-d800-4859-be49-624bbe60519d@gmail.com

This patch (of 2):

When ->readahead callback doesn't read all requested pages, read_pages()
shortens the readahead window (ra->size).  However we don't know why pages
were not read and what appropriate window size is.  So don't try to
secondguess the filesystem.  If it needs different readahead window, it
should set it manually similarly as during expansion the filesystem can
use readahead_expand().

Link: https://lkml.kernel.org/r/20241204181016.15273-1-jack@suse.cz
Link: https://lkml.kernel.org/r/20241204181016.15273-2-jack@suse.cz


Signed-off-by: default avatarJan Kara <jack@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarTong Tiangen <tongtiangen@huawei.com>
parent e1365f54

mm/readahead.c

+2 −12
Original line number Diff line number Diff line
@@ -164,20 +164,10 @@ static void read_pages(struct readahead_control *rac) 


	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.

		 */

		/* Clean up the remaining folios. */

		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);

		}