From: "Matthew Wilcox (Oracle)" willy@infradead.org
mainline inclusion from mainline-5.19-rc4 commit 5ccc944dce3df5fd2fd683a7df4fd49d1068eba2 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I6YDHU CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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We had an off-by-one error which meant that we never marked the first page in a read as accessed. This was visible as a slowdown when re-reading a file as pages were being evicted from cache too soon. In reviewing this code, we noticed a second bug where a multi-page folio would be marked as accessed multiple times when doing reads that were less than the size of the folio.
Abstract the comparison of whether two file positions are in the same folio into a new function, fixing both of these bugs.
Reported-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Kent Overstreet kent.overstreet@gmail.com Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org
Conflict: folios is not supported yet Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Jialin Zhang zhangjialin11@huawei.com --- mm/filemap.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c index 173c2962b16a..5ac55c3f19f7 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2530,6 +2530,13 @@ static int generic_file_buffered_read_get_pages(struct kiocb *iocb, goto find_page; }
+static inline bool pos_same_page(loff_t pos1, loff_t pos2, struct page *page) +{ + unsigned int shift = page_shift(page); + + return (pos1 >> shift == pos2 >> shift); +} + /** * generic_file_buffered_read - generic file read routine * @iocb: the iocb to read @@ -2620,11 +2627,10 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, writably_mapped = mapping_writably_mapped(mapping);
/* - * When a sequential read accesses a page several times, only + * When a read accesses a page several times, only * mark it as accessed the first time. */ - if (iocb->ki_pos >> PAGE_SHIFT != - ra->prev_pos >> PAGE_SHIFT) + if (!pos_same_page(iocb->ki_pos, ra->prev_pos -1, pages[0])) mark_page_accessed(pages[0]); for (i = 1; i < pg_nr; i++) mark_page_accessed(pages[i]);