From: Yu Kuai yukuai3@huawei.com
[ Upstream commit 257ac239ffcfd097a9a0732bf5095fb00164f334 ]
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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 456d745eb93b3..82c9bb404ccca 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -601,13 +601,12 @@ 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 @@ -618,11 +617,11 @@ 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) || @@ -715,7 +714,6 @@ 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 @@ -734,15 +732,22 @@ 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; @@ -754,6 +759,13 @@ 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