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From:   Song Liu <song@kernel.org>
Date:   Mon, 9 Oct 2023 16:33:22 -0700
Message-ID: <CAPhsuW5Lv4SEJtVmH2AO1b0cNxErqazHH8Ew7jXt784rR59c8g@mail.gmail.com>
Subject: Re: [PATCH -next] md/raid1: don't split discard io for write behind
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com
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On Fri, Oct 6, 2023 at 8:24=E2=80=AFPM Yu Kuai <yukuai1@huaweicloud.com> wr=
ote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Currently, discad io is treated the same as normal write io, and for
> write behind case, io size is limited to:
>
> BIO_MAX_VECS * (PAGE_SIZE >> 9)
>
> For 0.5KB sector size and 4KB PAGE_SIZE, this is just 1MB. For
> consequence, if 'WriteMostly' is set to one of the underlying disks,
> then diskcard io will be splited into 1MB and it will take a long time
> for the diskcard to finish.
>
> Fix this problem by disable write behind for discard io.
>
> Reported-by: Roman Mamedov <rm@romanrm.net>
> Closes: https://lore.kernel.org/all/6a1165f7-c792-c054-b8f0-1ad4f7b8ae01@=
ultracoder.org/
> Reported-and-tested-by: Kirill Kirilenko <kirill@ultracoder.org>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Applied to md-next. Thanks!

Song

> ---
>  drivers/md/raid1.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 3a78f79ee6d5..35d12948e0a9 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1345,6 +1345,7 @@ static void raid1_write_request(struct mddev *mddev=
, struct bio *bio,
>         int first_clone;
>         int max_sectors;
>         bool write_behind =3D false;
> +       bool is_discard =3D (bio_op(bio) =3D=3D REQ_OP_DISCARD);
>
>         if (mddev_is_clustered(mddev) &&
>              md_cluster_ops->area_resyncing(mddev, WRITE,
> @@ -1405,7 +1406,7 @@ static void raid1_write_request(struct mddev *mddev=
, struct bio *bio,
>                  * write-mostly, which means we could allocate write behi=
nd
>                  * bio later.
>                  */
> -               if (rdev && test_bit(WriteMostly, &rdev->flags))
> +               if (!is_discard && rdev && test_bit(WriteMostly, &rdev->f=
lags))
>                         write_behind =3D true;
>
>                 if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
> --
> 2.39.2
>