Messages in this thread | | | Subject | Re: [PATCH md-6.9 03/10] md/raid1: fix choose next idle in read_balance() | From | Yu Kuai <> | Date | Mon, 26 Feb 2024 17:40:05 +0800 |
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Hi,
在 2024/02/26 17:24, Xiao Ni 写道: > On Mon, Feb 26, 2024 at 5:12 PM Yu Kuai <yukuai1@huaweicloud.com> 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@huaweicloud.com> wrote: >>>> >>>> From: Yu Kuai <yukuai3@huawei.com> >>>> >>>> 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@linux.intel.com> >>>> Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com> >>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >>>> --- >>>> 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 >>>> >>>> >>> >>> . >>> >> > > . >
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