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readahead: fix return value of page_cache_next_miss() when no hole is found

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commit bbcaee20e0 upstream.

max_scan in page_cache_next_miss always decreases to zero when no hole is
found, causing the return value to be index + 0.

Fix this by preserving the max_scan value throughout the loop.

Jan said "From what I know and have seen in the past, wrong responses
from page_cache_next_miss() can lead to readahead window reduction and
thus reduced read speeds."

Link: https://lkml.kernel.org/r/20250605054935.2323451-1-chizhiling@163.com
Fixes: 901a269ff3 ("filemap: fix page_cache_next_miss() when no hole found")
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Chi Zhiling 2025-06-05 13:49:35 +08:00 committed by Greg Kroah-Hartman
parent 617a8d148d
commit 72e849b5b1
1 changed files with 2 additions and 1 deletions
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3
mm/filemap.c
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@ -1750,8 +1750,9 @@ pgoff_t page_cache_next_miss(struct address_space *mapping,
pgoff_t index, unsigned long max_scan)
{
XA_STATE(xas, &mapping->i_pages, index);
unsigned long nr = max_scan;
while (max_scan--) {
while (nr--) {
void *entry = xas_next(&xas);
if (!entry || xa_is_value(entry))
return xas.xa_index;