The patch titled
Subject: mm/filemap.c: fix the timing of asignment of prev_pos
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-filemapc-fix-the-timing-of-asignment-of-prev_pos.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-filemapc-fix-the-timing-of-asignment-of-prev_pos.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Guixin Liu <kanie@xxxxxxxxxxxxxxxxx>
Subject: mm/filemap.c: fix the timing of asignment of prev_pos
Date: Wed, 17 Aug 2022 21:51:57 +0800
When I`m running repetitive 4k read io which has same offset, I find that
access to folio_mark_accessed is inevitable in the read process, the
reason is that the prev_pos is assigned after the iocb->ki_pos is
incremented, so that the prev_pos is always not equal to the position
currently visited.
The prev_pos should be assigned before the iocb->ki_pos is incremented, so
that the prev_pos is the exact location of the last visit.
Link: https://lkml.kernel.org/r/1660744317-8183-1-git-send-email-kanie@xxxxxxxxxxxxxxxxx
Fixes: 06c0444290cec ("mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig")
Signed-off-by: Guixin Liu <kanie@xxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/filemap.c~mm-filemapc-fix-the-timing-of-asignment-of-prev_pos
+++ a/mm/filemap.c
@@ -2711,8 +2711,8 @@ ssize_t filemap_read(struct kiocb *iocb,
copied = copy_folio_to_iter(folio, offset, bytes, iter);
already_read += copied;
- iocb->ki_pos += copied;
ra->prev_pos = iocb->ki_pos;
+ iocb->ki_pos += copied;
if (copied < bytes) {
error = -EFAULT;
_
Patches currently in -mm which might be from kanie@xxxxxxxxxxxxxxxxx are
mm-filemapc-fix-the-timing-of-asignment-of-prev_pos.patch
