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Subject: [RFC PATCH 1/7] Fix khugepaged's request size in collapse_file()
From:   David Howells <dhowells@redhat.com>
To:     willy@infradead.org
Cc:     dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Date:   Tue, 01 Sep 2020 17:28:22 +0100
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collapse_file() in khugepaged passes PAGE_SIZE as the number of pages to be
read ahead to page_cache_sync_readahead().  It seems this was expressed as a
number of bytes rather than a number of pages.

Fix it to use the number of pages to the end of the window instead.

Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Song Liu <songliubraving@fb.com>
---

 mm/khugepaged.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6d199c353281..f2d243077b74 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1706,7 +1706,7 @@ static void collapse_file(struct mm_struct *mm,
 				xas_unlock_irq(&xas);
 				page_cache_sync_readahead(mapping, &file->f_ra,
 							  file, index,
-							  PAGE_SIZE);
+							  end - index);
 				/* drain pagevecs to help isolate_lru_page() */
 				lru_add_drain();
 				page = find_lock_page(mapping, index);