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blk-cgroup: Pre-allocate tree node on blkg_conf_prep 

Similarly to commit 457e490f2b ("blkcg: allocate struct blkcg_gq
outside request queue spinlock"), blkg_create can also trigger
occasional -ENOMEM failures at the radix insertion because any
allocation inside blkg_create has to be non-blocking, making it more
likely to fail.  This causes trouble for userspace tools trying to
configure io weights who need to deal with this condition.

This patch reduces the occurrence of -ENOMEMs on this path by preloading
the radix tree element on a GFP_KERNEL context, such that we guarantee
the later non-blocking insertion won't fail.

A similar solution exists in blkcg_init_queue for the same situation.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Gabriel Krisman Bertazi 2020-10-22 16:58:42 -04:00 committed by Jens Axboe
parent 52abfcbd57
commit f255c19b3a
1 changed files with 12 additions and 2 deletions
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14
block/blk-cgroup.c
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@ -657,6 +657,12 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
goto fail;
}
if (radix_tree_preload(GFP_KERNEL)) {
blkg_free(new_blkg);
ret = -ENOMEM;
goto fail;
}
rcu_read_lock();
spin_lock_irq(&q->queue_lock);
@ -664,7 +670,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
if (IS_ERR(blkg)) {
ret = PTR_ERR(blkg);
blkg_free(new_blkg);
goto fail_unlock;
goto fail_preloaded;
}
if (blkg) {
@ -673,10 +679,12 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
blkg = blkg_create(pos, q, new_blkg);
if (IS_ERR(blkg)) {
ret = PTR_ERR(blkg);
goto fail_unlock;
goto fail_preloaded;
}
}
radix_tree_preload_end();
if (pos == blkcg)
goto success;
}
@ -686,6 +694,8 @@ success:
ctx->body = input;
return 0;
fail_preloaded:
radix_tree_preload_end();
fail_unlock:
spin_unlock_irq(&q->queue_lock);
rcu_read_unlock();