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From:   Yang Shi <shy828301@gmail.com>
Date:   Wed, 2 Sep 2020 10:43:22 -0700
Message-ID: <CAHbLzkpL+657FqvvkATq8NiVwioeiovg=972RsktuW5n+3D+pg@mail.gmail.com>
Subject: Re: [PATCH] Fix khugepaged's request size in collapse_file()
To:     David Howells <dhowells@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Song Liu <songliubraving@fb.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Sep 2, 2020 at 7:16 AM David Howells <dhowells@redhat.com> wrote:
>
> 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>
> Acked-by: Song Liu <songliubraving@fb.com>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Yang Shi <shy828301@gmail.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);
>
>
>