linux-kernel - Re: [PATCH 1/3] md: align superblock writes to physical blocks

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Message-ID: <CAPhsuW50ON69Z=Wq30fEw0M2mGtXYKQCUNUbDS78AUe--nNZSg@mail.gmail.com>
Date:   Thu, 22 Oct 2020 22:46:17 -0700
From:   Song Liu <song@...nel.org>
To:     Christopher Unkel <cunkel@...vescale.com>
Cc:     linux-raid <linux-raid@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] md: align superblock writes to physical blocks

On Thu, Oct 22, 2020 at 8:31 PM Christopher Unkel <cunkel@...vescale.com> wrote:
>
> Writes of the md superblock are aligned to the logical blocks of the
> containing device, but no attempt is made to align them to physical
> block boundaries.  This means that on a "512e" device (4k physical, 512
> logical) every superblock update hits the 512-byte emulation and the
> possible associated performance penalty.
>
> Respect the physical block alignment when possible.
>
> Signed-off-by: Christopher Unkel <cunkel@...vescale.com>
> ---
>  drivers/md/md.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 98bac4f304ae..2b42850acfb3 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1732,6 +1732,21 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
>             && rdev->new_data_offset < sb_start + (rdev->sb_size/512))
>                 return -EINVAL;
>
> +       /* Respect physical block size if feasible. */
> +       bmask = queue_physical_block_size(rdev->bdev->bd_disk->queue)-1;
> +       if (!((rdev->sb_start * 512) & bmask) && (rdev->sb_size & bmask)) {
> +               int candidate_size = (rdev->sb_size | bmask) + 1;
> +
> +               if (minor_version) {
> +                       int sectors = candidate_size / 512;
> +
> +                       if (rdev->data_offset >= sb_start + sectors
> +                           && rdev->new_data_offset >= sb_start + sectors)
> +                               rdev->sb_size = candidate_size;
> +               } else if (bmask <= 4095)
> +                       rdev->sb_size = candidate_size;
> +       }

In super_1_load() and super_1_sync(), we have

    bmask = queue_logical_block_size(rdev->bdev->bd_disk->queue)-1;

I think we should replace it with queue_physical_block_size() so the logic is
cleaner. Would this work?

Thanks,
Song