From bbcaee20e03ecaeeecba32a703816a0d4502b6c4 Mon Sep 17 00:00:00 2001 From: Chi Zhiling Date: Thu, 5 Jun 2025 13:49:35 +0800 Subject: [PATCH] readahead: fix return value of page_cache_next_miss() when no hole is found 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: 901a269ff3d5 ("filemap: fix page_cache_next_miss() when no hole found") Signed-off-by: Chi Zhiling Reviewed-by: Jan Kara Cc: Josef Bacik Cc: Matthew Wilcox (Oracle) Cc: Signed-off-by: Andrew Morton --- mm/filemap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index bada249b9fb76..a6459874bb2aa 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1778,8 +1778,9 @@ 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; -- 2.47.2