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md/raid1: factor out helpers to choose the best rdev from read_balance()

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The way that best rdev is chosen:

1) If the read is sequential from one rdev:
 - if rdev is rotational, use this rdev;
 - if rdev is non-rotational, use this rdev until total read length
   exceed disk opt io size;

2) If the read is not sequential:
 - if there is idle disk, use it, otherwise:
 - if the array has non-rotational disk, choose the rdev with minimal
   inflight IO;
 - if all the underlaying disks are rotational disk, choose the rdev
   with closest IO;

There are no functional changes, just to make code cleaner and prepare
for following refactor.

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/20240229095714.926789-12-yukuai1@huaweicloud.com
This commit is contained in:
Yu Kuai 2024-02-29 17:57:14 +08:00 committed by Song Liu
parent ba58f57fdf
commit 0091c5a269
1 changed files with 102 additions and 81 deletions
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183
drivers/md/raid1.c
View File

@ -730,74 +730,71 @@ static bool should_choose_next(struct r1conf *conf, int disk)
mirror->next_seq_sect - opt_iosize >= mirror->seq_start;
}
/*
* This routine returns the disk from which the requested read should
* be done. There is a per-array 'next expected sequential IO' sector
* number - if this matches on the next IO then we use the last disk.
* There is also a per-disk 'last know head position' sector that is
* maintained from IRQ contexts, both the normal and the resync IO
* completion handlers update this position correctly. If there is no
* perfect sequential match then we pick the disk whose head is closest.
*
* If there are 2 mirrors in the same 2 devices, performance degrades
* because position is mirror, not device based.
*
* The rdev for the device selected will have nr_pending incremented.
*/
static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sectors)
static bool rdev_readable(struct md_rdev *rdev, struct r1bio *r1_bio)
{
if (!rdev || test_bit(Faulty, &rdev->flags))
return false;
/* still in recovery */
if (!test_bit(In_sync, &rdev->flags) &&
rdev->recovery_offset < r1_bio->sector + r1_bio->sectors)
return false;
/* don't read from slow disk unless have to */
if (test_bit(WriteMostly, &rdev->flags))
return false;
/* don't split IO for bad blocks unless have to */
if (rdev_has_badblock(rdev, r1_bio->sector, r1_bio->sectors))
return false;
return true;
}
struct read_balance_ctl {
sector_t closest_dist;
int closest_dist_disk;
int min_pending;
int min_pending_disk;
int sequential_disk;
int readable_disks;
};
static int choose_best_rdev(struct r1conf *conf, struct r1bio *r1_bio)
{
const sector_t this_sector = r1_bio->sector;
int sectors;
int best_good_sectors;
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;
retry:
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;
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);
struct read_balance_ctl ctl = {
.closest_dist_disk = -1,
.closest_dist = MaxSector,
.min_pending_disk = -1,
.min_pending = UINT_MAX,
.sequential_disk = -1,
};
for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
struct md_rdev *rdev;
sector_t dist;
unsigned int pending;
rdev = conf->mirrors[disk].rdev;
if (r1_bio->bios[disk] == IO_BLOCKED
|| rdev == NULL
|| test_bit(Faulty, &rdev->flags))
continue;
if (!test_bit(In_sync, &rdev->flags) &&
rdev->recovery_offset < this_sector + sectors)
continue;
if (test_bit(WriteMostly, &rdev->flags))
continue;
if (rdev_has_badblock(rdev, this_sector, sectors))
if (r1_bio->bios[disk] == IO_BLOCKED)
continue;
if (best_disk >= 0)
/* At least two disks to choose from so failfast is OK */
rdev = conf->mirrors[disk].rdev;
if (!rdev_readable(rdev, r1_bio))
continue;
/* At least two disks to choose from so failfast is OK */
if (ctl.readable_disks++ == 1)
set_bit(R1BIO_FailFast, &r1_bio->state);
pending = atomic_read(&rdev->nr_pending);
dist = abs(this_sector - conf->mirrors[disk].head_position);
dist = abs(r1_bio->sector - conf->mirrors[disk].head_position);
/* Don't change to another disk for sequential reads */
if (is_sequential(conf, disk, r1_bio)) {
if (!should_choose_next(conf, disk)) {
best_disk = disk;
break;
}
if (!should_choose_next(conf, disk))
return disk;
/*
* Add 'pending' to avoid choosing this disk if
* there is other idle disk.
@ -807,17 +804,17 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
* If there is no other idle disk, this disk
* will be chosen.
*/
sequential_disk = disk;
ctl.sequential_disk = disk;
}
if (min_pending > pending) {
min_pending = pending;
best_pending_disk = disk;
if (ctl.min_pending > pending) {
ctl.min_pending = pending;
ctl.min_pending_disk = disk;
}
if (dist < best_dist) {
best_dist = dist;
best_dist_disk = disk;
if (ctl.closest_dist > dist) {
ctl.closest_dist = dist;
ctl.closest_dist_disk = disk;
}
}
@ -825,8 +822,8 @@ 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 (ctl.sequential_disk != -1 && ctl.min_pending != 0)
return ctl.sequential_disk;
/*
* If all disks are rotational, choose the closest disk. If any disk is
@ -834,26 +831,50 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
* disk is rotational, which might/might not be optimal for raids with
* mixed ratation/non-rotational disks depending on workload.
*/
if (best_disk == -1) {
if (READ_ONCE(conf->nonrot_disks) || min_pending == 0)
best_disk = best_pending_disk;
else
best_disk = best_dist_disk;
if (ctl.min_pending_disk != -1 &&
(READ_ONCE(conf->nonrot_disks) || ctl.min_pending == 0))
return ctl.min_pending_disk;
else
return ctl.closest_dist_disk;
}
/*
* This routine returns the disk from which the requested read should be done.
*
* 1) If resync is in progress, find the first usable disk and use it even if it
* has some bad blocks.
*
* 2) Now that there is no resync, loop through all disks and skipping slow
* disks and disks with bad blocks for now. Only pay attention to key disk
* choice.
*
* 3) If we've made it this far, now look for disks with bad blocks and choose
* the one with most number of sectors.
*
* 4) If we are all the way at the end, we have no choice but to use a disk even
* if it is write mostly.
*
* The rdev for the device selected will have nr_pending incremented.
*/
static int read_balance(struct r1conf *conf, struct r1bio *r1_bio,
int *max_sectors)
{
int disk;
clear_bit(R1BIO_FailFast, &r1_bio->state);
if (raid1_should_read_first(conf->mddev, r1_bio->sector,
r1_bio->sectors))
return choose_first_rdev(conf, r1_bio, max_sectors);
disk = choose_best_rdev(conf, r1_bio);
if (disk >= 0) {
*max_sectors = r1_bio->sectors;
update_read_sectors(conf, disk, r1_bio->sector,
r1_bio->sectors);
return disk;
}
if (best_disk >= 0) {
rdev = conf->mirrors[best_disk].rdev;
if (!rdev)
goto retry;
sectors = best_good_sectors;
update_read_sectors(conf, disk, this_sector, sectors);
}
*max_sectors = sectors;
if (best_disk >= 0)
return best_disk;
/*
* If we are here it means we didn't find a perfectly good disk so
* now spend a bit more time trying to find one with the most good