On Tue, Feb 27, 2024 at 8:09 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Commit 12cee5a8a29e ("md/raid1: prevent merging too large request") add
> the case choose next idle in read_balance():
>
> read_balance:
> for_each_rdev
> if(next_seq_sect == this_sector || dist == 0)
> -> sequential reads
> best_disk = disk;
> if (...)
> choose_next_idle = 1
> continue;
>
> for_each_rdev
> -> iterate next rdev
> if (pending == 0)
> best_disk = disk;
> -> choose the next idle disk
> break;
>
> if (choose_next_idle)
> -> keep using this rdev if there are no other idle disk
> contine
>
> However, commit 2e52d449bcec ("md/raid1: add failfast handling for reads.")
> remove the code:
>
> - /* If device is idle, use it */
> - if (pending == 0) {
> - best_disk = disk;
> - break;
> - }
>
> Hence choose next idle will never work now, fix this problem by
> following:
>
> 1) don't set best_disk in this case, read_balance() will choose the best
> disk after iterating all the disks;
> 2) add 'pending' so that other idle disk will be chosen;
> 3) add a new local variable 'sequential_disk' to record the disk, and if
> there is no other idle disk, 'sequential_disk' will be chosen;
>
> Fixes: 2e52d449bcec ("md/raid1: add failfast handling for reads.")
> 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 | 32 ++++++++++++++++++++++----------
> 1 file changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 0fed01b06de9..fc5899fb08c1 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -598,13 +598,12 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> const sector_t this_sector = r1_bio->sector;
> int sectors;
> int best_good_sectors;
> - int best_disk, best_dist_disk, best_pending_disk;
> + int best_disk, best_dist_disk, best_pending_disk, sequential_disk;
> int disk;
> sector_t best_dist;
> unsigned int min_pending;
> struct md_rdev *rdev;
> int choose_first;
> - int choose_next_idle;
>
> /*
> * Check if we can balance. We can balance on the whole
> @@ -615,11 +614,11 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> sectors = r1_bio->sectors;
> best_disk = -1;
> best_dist_disk = -1;
> + sequential_disk = -1;
> best_dist = MaxSector;
> best_pending_disk = -1;
> min_pending = UINT_MAX;
> best_good_sectors = 0;
> - choose_next_idle = 0;
> clear_bit(R1BIO_FailFast, &r1_bio->state);
>
> if ((conf->mddev->recovery_cp < this_sector + sectors) ||
> @@ -712,7 +711,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;
> struct raid1_info *mirror = &conf->mirrors[disk];
>
> - best_disk = disk;
> /*
> * If buffered sequential IO size exceeds optimal
> * iosize, check if there is idle disk. If yes, choose
> @@ -731,15 +729,22 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> mirror->next_seq_sect > opt_iosize &&
> mirror->next_seq_sect - opt_iosize >=
> mirror->seq_start) {
> - choose_next_idle = 1;
> - continue;
> + /*
> + * Add 'pending' to avoid choosing this disk if
> + * there is other idle disk.
> + */
> + pending++;
> + /*
> + * If there is no other idle disk, this disk
> + * will be chosen.
> + */
> + sequential_disk = disk;
> + } else {
> + best_disk = disk;
> + break;
> }
> - break;
> }
>
> - if (choose_next_idle)
> - continue;
> -
> if (min_pending > pending) {
> min_pending = pending;
> best_pending_disk = disk;
> @@ -751,6 +756,13 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> }
> }
>
> + /*
> + * sequential IO size exceeds optimal iosize, however, there is no other
> + * idle disk, so choose the sequential disk.
> + */
> + if (best_disk == -1 && min_pending != 0)
> + best_disk = sequential_disk;
> +
> /*
> * If all disks are rotational, choose the closest disk. If any disk is
> * non-rotational, choose the disk with less pending request even the
> --
> 2.39.2
>
Hi all
This patch looks good to me.
Reviewed-by: Xiao Ni <xni@xxxxxxxxxx>
