blkcg: convert blkg_lookup_create() to find closest blkg

There are several scenarios where blkg_lookup_create() can fail such as
the blkcg dying, request_queue is dying, or simply being OOM. Most
handle this by simply falling back to the q->root_blkg and calling it a
day.

This patch implements the notion of closest blkg. During
blkg_lookup_create(), if it fails to create, return the closest blkg
found or the q->root_blkg. blkg_try_get_closest() is introduced and used
during association so a bio is always attached to a blkg.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dennis Zhou 2018-12-05 12:10:28 -05:00 committed by Jens Axboe
parent b978962ad4
commit beea9da07d
5 changed files with 43 additions and 37 deletions

View File

@ -2009,21 +2009,24 @@ int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css)
EXPORT_SYMBOL_GPL(bio_associate_blkcg);
/**
* bio_associate_blkg - associate a bio with the specified blkg
* bio_associate_blkg - associate a bio with the a blkg
* @bio: target bio
* @blkg: the blkg to associate
*
* Associate @bio with the blkg specified by @blkg. This is the queue specific
* blkcg information associated with the @bio, a reference will be taken on the
* @blkg and will be freed when the bio is freed.
* This tries to associate @bio with the specified @blkg. Association failure
* is handled by walking up the blkg tree. Therefore, the blkg associated can
* be anything between @blkg and the root_blkg. This situation only happens
* when a cgroup is dying and then the remaining bios will spill to the closest
* alive blkg.
*
* A reference will be taken on the @blkg and will be released when @bio is
* freed.
*/
int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
{
if (unlikely(bio->bi_blkg))
return -EBUSY;
if (!blkg_try_get(blkg))
return -ENODEV;
bio->bi_blkg = blkg;
bio->bi_blkg = blkg_try_get_closest(blkg);
return 0;
}

View File

@ -258,9 +258,8 @@ err_free_blkg:
* that all non-root blkg's have access to the parent blkg. This function
* should be called under RCU read lock and @q->queue_lock.
*
* Returns pointer to the looked up or created blkg on success, ERR_PTR()
* value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
* dead and bypassing, returns ERR_PTR(-EBUSY).
* Returns the blkg or the closest blkg if blkg_create() fails as it walks
* down from root.
*/
struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
@ -276,19 +275,29 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
/*
* Create blkgs walking down from blkcg_root to @blkcg, so that all
* non-root blkgs have access to their parents.
* non-root blkgs have access to their parents. Returns the closest
* blkg to the intended blkg should blkg_create() fail.
*/
while (true) {
struct blkcg *pos = blkcg;
struct blkcg *parent = blkcg_parent(blkcg);
struct blkcg_gq *ret_blkg = q->root_blkg;
while (parent && !__blkg_lookup(parent, q, false)) {
while (parent) {
blkg = __blkg_lookup(parent, q, false);
if (blkg) {
/* remember closest blkg */
ret_blkg = blkg;
break;
}
pos = parent;
parent = blkcg_parent(parent);
}
blkg = blkg_create(pos, q, NULL);
if (pos == blkcg || IS_ERR(blkg))
if (IS_ERR(blkg))
return ret_blkg;
if (pos == blkcg)
return blkg;
}
}

View File

@ -483,21 +483,11 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
rcu_read_lock();
bio_associate_blkcg(bio, NULL);
blkcg = bio_blkcg(bio);
blkg = blkg_lookup(blkcg, q);
if (unlikely(!blkg)) {
spin_lock_irq(&q->queue_lock);
blkg = __blkg_lookup_create(blkcg, q);
if (IS_ERR(blkg))
blkg = NULL;
spin_unlock_irq(&q->queue_lock);
}
if (!blkg)
goto out;
blkg = blkg_lookup_create(blkcg, q);
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
bio_associate_blkg(bio, blkg);
out:
rcu_read_unlock();
while (blkg && blkg->parent) {
struct iolatency_grp *iolat = blkg_to_lat(blkg);
if (!iolat) {

View File

@ -2118,9 +2118,7 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td)
static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio)
{
#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
/* fallback to root_blkg if we fail to get a blkg ref */
if (bio->bi_css && (bio_associate_blkg(bio, tg_to_blkg(tg)) == -ENODEV))
bio_associate_blkg(bio, bio->bi_disk->queue->root_blkg);
bio_associate_blkg(bio, tg_to_blkg(tg));
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
#endif
}

View File

@ -545,6 +545,20 @@ static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
return NULL;
}
/**
* blkg_try_get_closest - try and get a blkg ref on the closet blkg
* @blkg: blkg to get
*
* This walks up the blkg tree to find the closest non-dying blkg and returns
* the blkg that it did association with as it may not be the passed in blkg.
*/
static inline struct blkcg_gq *blkg_try_get_closest(struct blkcg_gq *blkg)
{
while (!atomic_inc_not_zero(&blkg->refcnt))
blkg = blkg->parent;
return blkg;
}
void __blkg_release_rcu(struct rcu_head *rcu);
@ -797,15 +811,7 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
/* associate blkcg if bio hasn't attached one */
bio_associate_blkcg(bio, NULL);
blkcg = bio_blkcg(bio);
blkg = blkg_lookup(blkcg, q);
if (unlikely(!blkg)) {
spin_lock_irq(&q->queue_lock);
blkg = __blkg_lookup_create(blkcg, q);
if (IS_ERR(blkg))
blkg = NULL;
spin_unlock_irq(&q->queue_lock);
}
blkg = blkg_lookup_create(blkcg, q);
throtl = blk_throtl_bio(q, blkg, bio);