linux-kernel - Re: [PATCH 09/23] md/md-bitmap: add a new method blocks_synced() in bitmap

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Message-ID: <CALTww2_SUyLUFzQgLe+z0UFmcS72o1JDEkPfR5FEsOmj8CDsXw@mail.gmail.com>
Date: Tue, 27 May 2025 10:35:52 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: hch@....de, colyli@...nel.org, song@...nel.org, yukuai3@...wei.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-raid@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com, 
	johnny.chenyi@...wei.com
Subject: Re: [PATCH 09/23] md/md-bitmap: add a new method blocks_synced() in bitmap_operations

On Sat, May 24, 2025 at 2:18 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> Currently, raid456 must perform a whole array initial recovery to build
> initail xor data, then IO to the array won't have to read all the blocks
> in underlying disks.
>
> This behavior will affect IO performance a lot, and nowadays there are
> huge disks and the initial recovery can take a long time. Hence llbitmap
> will support lazy initial recovery in following patches. This method is
> used to check if data blocks is synced or not, if not then IO will still
> have to read all blocks for raid456.

Hi Kuai

In function handle_stripe_dirtying, if the io is behind resync, it
will force rcw. Does this interface have the same function？

Regards
Xiao
>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/md/md-bitmap.h | 1 +
>  drivers/md/raid5.c     | 6 ++++++
>  2 files changed, 7 insertions(+)
>
> diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h
> index 0de14d475ad3..f2d79c8a23b7 100644
> --- a/drivers/md/md-bitmap.h
> +++ b/drivers/md/md-bitmap.h
> @@ -99,6 +99,7 @@ struct bitmap_operations {
>         md_bitmap_fn *end_discard;
>
>         sector_t (*skip_sync_blocks)(struct mddev *mddev, sector_t offset);
> +       bool (*blocks_synced)(struct mddev *mddev, sector_t offset);
>         bool (*start_sync)(struct mddev *mddev, sector_t offset,
>                            sector_t *blocks, bool degraded);
>         void (*end_sync)(struct mddev *mddev, sector_t offset, sector_t *blocks);
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 7e66a99f29af..e5d3d8facb4b 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3748,6 +3748,7 @@ static int want_replace(struct stripe_head *sh, int disk_idx)
>  static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
>                            int disk_idx, int disks)
>  {
> +       struct mddev *mddev = sh->raid_conf->mddev;
>         struct r5dev *dev = &sh->dev[disk_idx];
>         struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
>                                   &sh->dev[s->failed_num[1]] };
> @@ -3762,6 +3763,11 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
>                  */
>                 return 0;
>
> +       /* The initial recover is not done, must read everything */
> +       if (mddev->bitmap_ops && mddev->bitmap_ops->blocks_synced &&
> +           !mddev->bitmap_ops->blocks_synced(mddev, sh->sector))
> +               return 1;
> +
>         if (dev->toread ||
>             (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)))
>                 /* We need this block to directly satisfy a request */
> --
> 2.39.2
>