| Message ID | 20210707015649.1929797-1-yukuai3@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V2] blk-cgroup: prevent rcu_sched detected stalls warnings while iterating blkgs | expand |
On Wed, Jul 07, 2021 at 09:56:49AM +0800, Yu Kuai wrote: > We run a test that create millions of cgroups and blkgs, and then trigger > blkg_destroy_all(). blkg_destroy_all() will hold spin lock for a long > time in such situation. Thus release the lock when a batch of blkgs are > destroyed. > > blkcg_activate_policy() and blkcg_deactivate_policy() might have the > same problem, however, as they are basically only called from module > init/exit paths, let's leave them alone for now. > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> Acked-by: Tejun Heo <tj@kernel.org> Thanks.
On 7/6/21 7:56 PM, Yu Kuai wrote: > We run a test that create millions of cgroups and blkgs, and then trigger > blkg_destroy_all(). blkg_destroy_all() will hold spin lock for a long > time in such situation. Thus release the lock when a batch of blkgs are > destroyed. > > blkcg_activate_policy() and blkcg_deactivate_policy() might have the > same problem, however, as they are basically only called from module > init/exit paths, let's leave them alone for now. Applied, thanks.
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 7b06a5fa3cac..575d7a2e7203 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -56,6 +56,8 @@ static LIST_HEAD(all_blkcgs); /* protected by blkcg_pol_mutex */ bool blkcg_debug_stats = false; static struct workqueue_struct *blkcg_punt_bio_wq; +#define BLKG_DESTROY_BATCH_SIZE 64 + static bool blkcg_policy_enabled(struct request_queue *q, const struct blkcg_policy *pol) { @@ -422,7 +424,9 @@ static void blkg_destroy(struct blkcg_gq *blkg) static void blkg_destroy_all(struct request_queue *q) { struct blkcg_gq *blkg, *n; + int count = BLKG_DESTROY_BATCH_SIZE; +restart: spin_lock_irq(&q->queue_lock); list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) { struct blkcg *blkcg = blkg->blkcg; @@ -430,6 +434,17 @@ static void blkg_destroy_all(struct request_queue *q) spin_lock(&blkcg->lock); blkg_destroy(blkg); spin_unlock(&blkcg->lock); + + /* + * in order to avoid holding the spin lock for too long, release + * it when a batch of blkgs are destroyed. + */ + if (!(--count)) { + count = BLKG_DESTROY_BATCH_SIZE; + spin_unlock_irq(&q->queue_lock); + cond_resched(); + goto restart; + } } q->root_blkg = NULL;
We run a test that create millions of cgroups and blkgs, and then trigger blkg_destroy_all(). blkg_destroy_all() will hold spin lock for a long time in such situation. Thus release the lock when a batch of blkgs are destroyed. blkcg_activate_policy() and blkcg_deactivate_policy() might have the same problem, however, as they are basically only called from module init/exit paths, let's leave them alone for now. Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- changes in V2: - as suggested by Tejun, rename 'BLKG_DESTROY_BATCH_SIZE' and modify blkg_destroy_all() only. block/blk-cgroup.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)