Re: [PATCH md-6.9 06/10] md/raid1: factor out read_first_rdev() from read_balance()

[Xiao Ni]

On Thu, Feb 22, 2024 at 4:04 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> read_balance() is hard to understand because there are too many status
> and branches, and it's overlong.
>
> This patch factor out the case to read the first rdev from
> read_balance(), there are no functional changes.
>
> Co-developed-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
> Signed-off-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>  drivers/md/raid1.c | 63 +++++++++++++++++++++++++++++++++-------------
>  1 file changed, 46 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 8089c569e84f..08c45ca55a7e 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -579,6 +579,47 @@ static sector_t align_to_barrier_unit_end(sector_t start_sector,
>         return len;
>  }
>
> +static void update_read_sectors(struct r1conf *conf, int disk,
> +                               sector_t this_sector, int len)
> +{
> +       struct raid1_info *info = &conf->mirrors[disk];
> +
> +       atomic_inc(&info->rdev->nr_pending);
> +       if (info->next_seq_sect != this_sector)
> +               info->seq_start = this_sector;
> +       info->next_seq_sect = this_sector + len;
> +}
> +
> +static int choose_first_rdev(struct r1conf *conf, struct r1bio *r1_bio,
> +                            int *max_sectors)
> +{
> +       sector_t this_sector = r1_bio->sector;
> +       int len = r1_bio->sectors;
> +       int disk;
> +
> +       for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
> +               struct md_rdev *rdev;
> +               int read_len;
> +
> +               if (r1_bio->bios[disk] == IO_BLOCKED)
> +                       continue;
> +
> +               rdev = conf->mirrors[disk].rdev;
> +               if (!rdev || test_bit(Faulty, &rdev->flags))
> +                       continue;
> +
> +               /* choose the first disk even if it has some bad blocks. */
> +               read_len = raid1_check_read_range(rdev, this_sector, &len);
> +               if (read_len > 0) {
> +                       update_read_sectors(conf, disk, this_sector, read_len);
> +                       *max_sectors = read_len;
> +                       return disk;
> +               }
> +       }
> +
> +       return -1;
> +}
> +
>  /*
>   * This routine returns the disk from which the requested read should
>   * be done. There is a per-array 'next expected sequential IO' sector
> @@ -603,7 +644,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>         sector_t best_dist;
>         unsigned int min_pending;
>         struct md_rdev *rdev;
> -       int choose_first;
>
>   retry:
>         sectors = r1_bio->sectors;
> @@ -613,10 +653,11 @@ 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 (raid1_should_read_first(conf->mddev, this_sector, sectors))
> +               return choose_first_rdev(conf, r1_bio, max_sectors);
> +
>         for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
>                 sector_t dist;
>                 sector_t first_bad;
> @@ -662,8 +703,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                                  * bad_sectors from another device..
>                                  */
>                                 bad_sectors -= (this_sector - first_bad);
> -                               if (choose_first && sectors > bad_sectors)
> -                                       sectors = bad_sectors;
>                                 if (best_good_sectors > sectors)
>                                         best_good_sectors = sectors;
>
> @@ -673,8 +712,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                                         best_good_sectors = good_sectors;
>                                         best_disk = disk;
>                                 }
> -                               if (choose_first)
> -                                       break;
>                         }
>                         continue;
>                 } else {
> @@ -689,10 +726,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>
>                 pending = atomic_read(&rdev->nr_pending);
>                 dist = abs(this_sector - conf->mirrors[disk].head_position);
> -               if (choose_first) {
> -                       best_disk = disk;
> -                       break;
> -               }
>                 /* Don't change to another disk for sequential reads */
>                 if (conf->mirrors[disk].next_seq_sect == this_sector
>                     || dist == 0) {
> @@ -760,13 +793,9 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                 rdev = conf->mirrors[best_disk].rdev;
>                 if (!rdev)
>                         goto retry;
> -               atomic_inc(&rdev->nr_pending);
> -               sectors = best_good_sectors;
> -
> -               if (conf->mirrors[best_disk].next_seq_sect != this_sector)
> -                       conf->mirrors[best_disk].seq_start = this_sector;
>
> -               conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
> +               sectors = best_good_sectors;
> +               update_read_sectors(conf, disk, this_sector, sectors);
>         }
>         *max_sectors = sectors;
>
> --
> 2.39.2
>
>
Hi
This patch looks good to me.
Reviewed-by: Xiao Ni <xni@xxxxxxxxxx>