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/revert-readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra.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: Jan Kara <jack@xxxxxxx>
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@xxxxxxx
Fixes: 7c877586da31 ("readahead: properly shorten readahead when falling back to do_page_cache_ra()")
Reported-by: Anders Blomdell <anders.blomdell@xxxxxxxxx>
Reported-by: Philippe Troin <phil@xxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Tested-by: Philippe Troin <phil@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxx are
revert-readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra.patch
