linux-kernel - Re: [PATCH md-6.9 05/10] md/raid1-10: factor out a new helper raid1_should_read

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Date: Mon, 26 Feb 2024 21:46:49 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: paul.e.luse@...ux.intel.com, song@...nel.org, neilb@...e.com, shli@...com, 
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org, yukuai3@...wei.com, 
	yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH md-6.9 05/10] md/raid1-10: factor out a new helper raid1_should_read_first()

On Thu, Feb 22, 2024 at 4:05 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> If resync is in progress, read_balance() should find the first usable
> disk, otherwise, data could be inconsistent after resync is done. raid1
> and raid10 implement the same checking, hence factor out the checking
> to make code cleaner.
>
> Noted that raid1 is using 'mddev->recovery_cp', which is updated after
> all resync IO is done, while raid10 is using 'conf->next_resync', which
> is inaccurate because raid10 update it before submitting resync IO.
> Fortunately, raid10 read IO can't concurrent with resync IO, hence there
> is no problem. And this patch also switch raid10 to use
> 'mddev->recovery_cp'.
>
> Co-developed-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>  drivers/md/raid1-10.c | 20 ++++++++++++++++++++
>  drivers/md/raid1.c    | 15 ++-------------
>  drivers/md/raid10.c   | 13 ++-----------
>  3 files changed, 24 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/md/raid1-10.c b/drivers/md/raid1-10.c
> index 9bc0f0022a6c..2ea1710a3b70 100644
> --- a/drivers/md/raid1-10.c
> +++ b/drivers/md/raid1-10.c
> @@ -276,3 +276,23 @@ static inline int raid1_check_read_range(struct md_rdev *rdev,
>         *len = first_bad + bad_sectors - this_sector;
>         return 0;
>  }
> +
> +/*
> + * Check if read should choose the first rdev.
> + *
> + * Balance on the whole device if no resync is going on (recovery is ok) or
> + * below the resync window. Otherwise, take the first readable disk.
> + */
> +static inline bool raid1_should_read_first(struct mddev *mddev,
> +                                          sector_t this_sector, int len)
> +{
> +       if ((mddev->recovery_cp < this_sector + len))
> +               return true;
> +
> +       if (mddev_is_clustered(mddev) &&
> +           md_cluster_ops->area_resyncing(mddev, READ, this_sector,
> +                                          this_sector + len))
> +               return true;
> +
> +       return false;
> +}
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index d0bc67e6d068..8089c569e84f 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -605,11 +605,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>         struct md_rdev *rdev;
>         int choose_first;
>
> -       /*
> -        * Check if we can balance. We can balance on the whole
> -        * device if no resync is going on, or below the resync window.
> -        * We take the first readable disk when above the resync window.
> -        */
>   retry:
>         sectors = r1_bio->sectors;
>         best_disk = -1;
> @@ -618,16 +613,10 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>         best_pending_disk = -1;
>         min_pending = UINT_MAX;
>         best_good_sectors = 0;
> +       choose_first = raid1_should_read_first(conf->mddev, this_sector,
> +                                              sectors);
>         clear_bit(R1BIO_FailFast, &r1_bio->state);
>
> -       if ((conf->mddev->recovery_cp < this_sector + sectors) ||
> -           (mddev_is_clustered(conf->mddev) &&
> -           md_cluster_ops->area_resyncing(conf->mddev, READ, this_sector,
> -                   this_sector + sectors)))
> -               choose_first = 1;
> -       else
> -               choose_first = 0;
> -
>         for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
>                 sector_t dist;
>                 sector_t first_bad;
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 1f6693e40e12..22bcc3ce11d3 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -747,17 +747,8 @@ static struct md_rdev *read_balance(struct r10conf *conf,
>         best_good_sectors = 0;
>         do_balance = 1;
>         clear_bit(R10BIO_FailFast, &r10_bio->state);
> -       /*
> -        * Check if we can balance. We can balance on the whole
> -        * device if no resync is going on (recovery is ok), or below
> -        * the resync window. We take the first readable disk when
> -        * above the resync window.
> -        */
> -       if ((conf->mddev->recovery_cp < MaxSector
> -            && (this_sector + sectors >= conf->next_resync)) ||
> -           (mddev_is_clustered(conf->mddev) &&
> -            md_cluster_ops->area_resyncing(conf->mddev, READ, this_sector,
> -                                           this_sector + sectors)))
> +
> +       if (raid1_should_read_first(conf->mddev, this_sector, sectors))
>                 do_balance = 0;
>
>         for (slot = 0; slot < conf->copies ; slot++) {
> --
> 2.39.2
>
>

This patch looks good to me.
Reviewed-by: Xiao Ni <xni@...hat.com>