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From:   Yang Shi <shy828301@gmail.com>
Date:   Thu, 17 Oct 2019 14:46:38 -0700
Message-ID: <CAHbLzkoTT4p9u__EdFgt7_47NHOV5r=nB8EmvBx+1TcyzX5RJg@mail.gmail.com>
Subject: Re: [PATCH v2 4/5] mm/thp: allow drop THP from page cache
To:     Song Liu <songliubraving@fb.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        matthew.wilcox@oracle.com, kernel-team@fb.com,
        william.kucharski@oracle.com,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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On Thu, Oct 17, 2019 at 9:42 AM Song Liu <songliubraving@fb.com> wrote:
>
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> Once a THP is added to the page cache, it cannot be dropped via
> /proc/sys/vm/drop_caches. Fix this issue with proper handling in
> invalidate_mapping_pages().
>
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Tested-by: Song Liu <songliubraving@fb.com>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  mm/truncate.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 8563339041f6..dd9ebc1da356 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -592,6 +592,16 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>                                         unlock_page(page);
>                                         continue;
>                                 }
> +
> +                               /* Take a pin outside pagevec */
> +                               get_page(page);
> +
> +                               /*
> +                                * Drop extra pins before trying to invalidate
> +                                * the huge page.
> +                                */
> +                               pagevec_remove_exceptionals(&pvec);
> +                               pagevec_release(&pvec);

Shall we skip the outer pagevec_remove_exceptions() if it has been done here?

>                         }
>
>                         ret = invalidate_inode_page(page);
> @@ -602,6 +612,8 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>                          */
>                         if (!ret)
>                                 deactivate_file_page(page);
> +                       if (PageTransHuge(page))
> +                               put_page(page);
>                         count += ret;
>                 }
>                 pagevec_remove_exceptionals(&pvec);
> --
> 2.17.1
>
>