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md/raid1: fix choose next idle in read_balance()

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Commit 12cee5a8a2 ("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 2e52d449bc ("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: 2e52d449bc ("md/raid1: add failfast handling for reads.")
Co-developed-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240229095714.926789-5-yukuai1@huaweicloud.com
This commit is contained in:
Yu Kuai 2024-02-29 17:57:07 +08:00 committed by Song Liu
parent 2c27d09d3a
commit 257ac239ff
1 changed files with 22 additions and 10 deletions
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32
drivers/md/raid1.c
View File

@ -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
@ -731,14 +729,21 @@ 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;
}
if (choose_next_idle)
continue;
}
if (min_pending > pending) {
min_pending = pending;
@ -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