| From: Guixin Liu <kanie@linux.alibaba.com> |
| 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@linux.alibaba.com |
| Fixes: 06c0444290cec ("mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig") |
| Signed-off-by: Guixin Liu <kanie@linux.alibaba.com> |
| Cc: Matthew Wilcox <willy@infradead.org> |
| Cc: Kent Overstreet <kent.overstreet@gmail.com> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| 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; |
| _ |
