The patch titled Subject: Revert "readahead: properly shorten readahead when falling back to do_page_cache_ra()" has been added to the -mm mm-hotfixes-unstable branch. Its filename is revert-readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Jan Kara jack@suse.cz Subject: Revert "readahead: properly shorten readahead when falling back to do_page_cache_ra()" Date: Tue, 26 Nov 2024 15:52:08 +0100

This reverts commit 7c877586da3178974a8a94577b6045a48377ff25.

Anders and Philippe have reported that recent kernels occasionally hang when used with NFS in readahead code. The problem has been bisected to 7c877586da3 ("readahead: properly shorten readahead when falling back to do_page_cache_ra()"). The cause of the problem is that ra->size can be shrunk by read_pages() call and subsequently we end up calling do_page_cache_ra() with negative (read huge positive) number of pages. Let's revert 7c877586da3 for now until we can find a proper way how the logic in read_pages() and page_cache_ra_order() can coexist. This can lead to reduced readahead throughput due to readahead window confusion but that's better than outright hangs.

Link: https://lkml.kernel.org/r/20241126145208.985-1-jack@suse.cz Fixes: 7c877586da31 ("readahead: properly shorten readahead when falling back to do_page_cache_ra()") Reported-by: Anders Blomdell anders.blomdell@gmail.com Reported-by: Philippe Troin phil@fifi.org Signed-off-by: Jan Kara jack@suse.cz Tested-by: Philippe Troin phil@fifi.org Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/readahead.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/mm/readahead.c~revert-readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra +++ a/mm/readahead.c @@ -460,8 +460,7 @@ void page_cache_ra_order(struct readahea struct file_ra_state *ra, unsigned int new_order) { struct address_space *mapping = ractl->mapping; - pgoff_t start = readahead_index(ractl); - pgoff_t index = start; + pgoff_t index = readahead_index(ractl); unsigned int min_order = mapping_min_folio_order(mapping); pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT; pgoff_t mark = index + ra->size - ra->async_size; @@ -524,7 +523,7 @@ void page_cache_ra_order(struct readahea if (!err) return; fallback: - do_page_cache_ra(ractl, ra->size - (index - start), ra->async_size); + do_page_cache_ra(ractl, ra->size, ra->async_size); }

static unsigned long ractl_max_pages(struct readahead_control *ractl, _

Patches currently in -mm which might be from jack@suse.cz are

revert-readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra.patch