From: Jan Kara <jack@suse.cz> mainline inclusion from mainline-v6.14-rc1 commit d5ea5e5e50dffd13fccedb690a0a1f27be56191a category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBRWBB Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- When we succeed in creating some folios in page_cache_ra_order() but then need to fallback to single page folios, we don't shorten the amount to read passed to do_page_cache_ra() by the amount we've already read. This then results in reading more and also in placing another readahead mark in the middle of the readahead window which confuses readahead code. Fix the problem by properly reducing number of pages to read. Unlike previous attempt at this fix (commit 7c877586da31) which had to be reverted, we are now careful to check there is indeed something to read so that we don't submit negative-sized readahead. Link: https://lkml.kernel.org/r/20241204181016.15273-3-jack@suse.cz Signed-off-by: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: mm/readahead.c [context conflict, 26cfdb395eef("readahead: allocate folios with mapping_min_order in readahead") net merged] Signed-off-by: Tong Tiangen <tongtiangen@huawei.com> --- mm/readahead.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/mm/readahead.c b/mm/readahead.c index 7d36a29e1d68..69757a624982 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -487,7 +487,8 @@ void page_cache_ra_order(struct readahead_control *ractl, struct file_ra_state *ra, unsigned int new_order) { struct address_space *mapping = ractl->mapping; - pgoff_t index = readahead_index(ractl); + pgoff_t start = readahead_index(ractl); + pgoff_t index = start; pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT; pgoff_t mark = index + ra->size - ra->async_size; unsigned int nofs; @@ -546,12 +547,18 @@ void page_cache_ra_order(struct readahead_control *ractl, /* * If there were already pages in the page cache, then we may have * left some gaps. Let the regular readahead code take care of this - * situation. + * situation below. */ if (!err) return; fallback: - do_page_cache_ra(ractl, ra->size, ra->async_size); + /* + * ->readahead() may have updated readahead window size so we have to + * check there's still something to read. + */ + if (ra->size > index - start) + do_page_cache_ra(ractl, ra->size - (index - start), + ra->async_size); } /* -- 2.25.1