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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 22 Jul 2020 09:26:45 -0700
Message-ID: <CALvZod6zF7Ak8KWf4dq0pEF2ty7JN_SyNE7PxLjrfF+EuDbZ2w@mail.gmail.com>
Subject: Re: [PATCH 11/14] mm: use SWP_SYNCHRONOUS_IO more intelligently
To:     Christoph Hellwig <hch@lst.de>
Cc:     Jens Axboe <axboe@kernel.dk>, Song Liu <song@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Richard Weinberger <richard@nod.at>,
        Minchan Kim <minchan@kernel.org>,
        linux-mtd@lists.infradead.org, dm-devel@redhat.com,
        "open list:BLOCK LAYER" <linux-block@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, drbd-dev@lists.linbit.com,
        linux-raid@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Cgroups <cgroups@vger.kernel.org>
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On Tue, Jul 21, 2020 at 11:27 PM Christoph Hellwig <hch@lst.de> wrote:
>
> There is no point in trying to call bdev_read_page if SWP_SYNCHRONOUS_IO
> is not set, as the device won't support it.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  mm/page_io.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/mm/page_io.c b/mm/page_io.c
> index ccda7679008851..442061348dfb26 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -403,15 +403,17 @@ int swap_readpage(struct page *page, bool synchronous)
>                 goto out;
>         }
>
> -       ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
> -       if (!ret) {
> -               if (trylock_page(page)) {
> -                       swap_slot_free_notify(page);
> -                       unlock_page(page);
> -               }
> +       if (sis->flags & SWP_SYNCHRONOUS_IO) {
> +               ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
> +               if (ret) {

!ret

> +                       if (trylock_page(page)) {
> +                               swap_slot_free_notify(page);
> +                               unlock_page(page);
> +                       }
>
> -               count_vm_event(PSWPIN);
> -               goto out;
> +                       count_vm_event(PSWPIN);
> +                       goto out;
> +               }
>         }
>
>         ret = 0;
> --
> 2.27.0
>