Hi,
在 2024/02/26 17:24, Xiao Ni 写道:
On Mon, Feb 26, 2024 at 5:12 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/26 16:55, Xiao Ni 写道:
Hi Kuai
Thanks for the effort!
On Thu, Feb 22, 2024 at 4:04 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 || disk == 0)
typo error: s/disk/dist/g
-> 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
continue
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) set 'dist' to 0 so that if there is no other idle disk, and all disks
are rotational, this disk will still 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 | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index c60ea58ae8c5..d0bc67e6d068 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -604,7 +604,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
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
@@ -619,7 +618,6 @@ 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_next_idle = 0;
clear_bit(R1BIO_FailFast, &r1_bio->state);
if ((conf->mddev->recovery_cp < this_sector + sectors) ||
@@ -712,7 +710,6 @@ 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 +728,21 @@ 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.
+ * Set 'dist' to 0, so that if there is no other
+ * idle disk and all disks are rotational, this
+ * disk will still be chosen.
+ */
+ pending++;
+ dist = 0;
There is a problem. If all disks are not idle and there is a disk with
dist=0 before the seq disk, it can't read from the seq disk. It will
read from the first disk with dist=0. Maybe we can only add the codes
which are removed from 2e52d449bcec?
If there is a disk with disk=0, then best_dist_disk will be updated to
the disk, and best_dist will be updated to 0 already:
// in each iteration
if (dist < best_dist) {
best_dist = dist;
btest_disk_disk = disk;
}
In this case, best_dist will be set to the first disk with dist=0, and
at last, the disk will be chosen:
if (best_disk == -1) {
if (has_nonrot_disk || min_pending == 0)
best_disk = best_pending_disk;
else
best_disk = best_dist_disk;
-> the first disk with dist=0;
}
So, the problem that you concerned should not exist.
Hi Kuai
Thanks for the explanation. You're right. It chooses the first disk
which has dist==0. In the above, you made the same typo error disk=0
as the comment. I guess you want to use dist=0, right? Beside this,
this patch is good to me.
Yes, and Paul change the name 'best_dist' to 'closest_dist_disk',
and 'btest_disk_disk' to 'closest_dist' in the last patch to avoid typo
like this. :)
Thanks,
Kuai
Best Regards
Xiao
Thanks,
Kuai
Best Regards
Xiao
+ } else {
+ best_disk = disk;
+ break;
}
- break;
}
- if (choose_next_idle)
- continue;
-
if (min_pending > pending) {
min_pending = pending;
best_pending_disk = disk;
--
2.39.2
.
.
