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blk-cgroup: Allow sleeping while dynamically allocating a group
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Currently, all the cfq_group or throtl_group allocations happen while
we are holding ->queue_lock and sleeping is not allowed.

Soon, we will move to per cpu stats and also need to allocate the
per group stats. As one can not call alloc_percpu() from atomic
context as it can sleep, we need to drop ->queue_lock, allocate the
group, retake the lock and continue processing.

In throttling code, I check the queue DEAD flag again to make sure
that driver did not call blk_cleanup_queue() in the mean time.

Signed-off-by: Vivek Goyal <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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@rhvgoyal
rhvgoyal authored and Jens Axboe committed May 20, 2011
1 parent 56edf7d commit f469a7b
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Showing 3 changed files with 205 additions and 67 deletions.
3 changes: 2 additions & 1 deletion block/blk-core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1550,7 +1550,8 @@ static inline void __generic_make_request(struct bio *bio)
goto end_io;
}

blk_throtl_bio(q, &bio);
if (blk_throtl_bio(q, &bio))
goto end_io;

/*
* If bio = NULL, bio has been throttled and will be submitted
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141 changes: 108 additions & 33 deletions block/blk-throttle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -188,20 +188,46 @@ throtl_add_group_to_td_list(struct throtl_data *td, struct throtl_grp *tg)
td->nr_undestroyed_grps++;
}

static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
struct blkio_cgroup *blkcg)
static void throtl_init_add_tg_lists(struct throtl_data *td,
struct throtl_grp *tg, struct blkio_cgroup *blkcg)
{
struct backing_dev_info *bdi = &td->queue->backing_dev_info;
unsigned int major, minor;

/* Add group onto cgroup list */
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
MKDEV(major, minor), BLKIO_POLICY_THROTL);

tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);

throtl_add_group_to_td_list(td, tg);
}

/* Should be called without queue lock and outside of rcu period */
static struct throtl_grp *throtl_alloc_tg(struct throtl_data *td)
{
struct throtl_grp *tg = NULL;

tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
if (!tg)
return NULL;

throtl_init_group(tg);
return tg;
}

static struct
throtl_grp *throtl_find_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
{
struct throtl_grp *tg = NULL;
void *key = td;
struct backing_dev_info *bdi = &td->queue->backing_dev_info;
unsigned int major, minor;

/*
* TODO: Speed up blkiocg_lookup_group() by maintaining a radix
* tree of blkg (instead of traversing through hash list all
* the time.
*/

/*
* This is the common case when there are no blkio cgroups.
* Avoid lookup in this case
Expand All @@ -215,43 +241,83 @@ static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
tg->blkg.dev = MKDEV(major, minor);
goto done;
}

if (tg)
goto done;

tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
if (!tg)
goto done;

throtl_init_group(tg);

/* Add group onto cgroup list */
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
MKDEV(major, minor), BLKIO_POLICY_THROTL);

tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);

throtl_add_group_to_td_list(td, tg);
done:
return tg;
}

/*
* This function returns with queue lock unlocked in case of error, like
* request queue is no more
*/
static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
{
struct throtl_grp *tg = NULL;
struct throtl_grp *tg = NULL, *__tg = NULL;
struct blkio_cgroup *blkcg;
struct request_queue *q = td->queue;

rcu_read_lock();
blkcg = task_blkio_cgroup(current);
tg = throtl_find_alloc_tg(td, blkcg);
if (!tg)
tg = throtl_find_tg(td, blkcg);
if (tg) {
rcu_read_unlock();
return tg;
}

/*
* Need to allocate a group. Allocation of group also needs allocation
* of per cpu stats which in-turn takes a mutex() and can block. Hence
* we need to drop rcu lock and queue_lock before we call alloc
*
* Take the request queue reference to make sure queue does not
* go away once we return from allocation.
*/
blk_get_queue(q);
rcu_read_unlock();
spin_unlock_irq(q->queue_lock);

tg = throtl_alloc_tg(td);
/*
* We might have slept in group allocation. Make sure queue is not
* dead
*/
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
blk_put_queue(q);
if (tg)
kfree(tg);

return ERR_PTR(-ENODEV);
}
blk_put_queue(q);

/* Group allocated and queue is still alive. take the lock */
spin_lock_irq(q->queue_lock);

/*
* Initialize the new group. After sleeping, read the blkcg again.
*/
rcu_read_lock();
blkcg = task_blkio_cgroup(current);

/*
* If some other thread already allocated the group while we were
* not holding queue lock, free up the group
*/
__tg = throtl_find_tg(td, blkcg);

if (__tg) {
kfree(tg);
rcu_read_unlock();
return __tg;
}

/* Group allocation failed. Account the IO to root group */
if (!tg) {
tg = &td->root_tg;
return tg;
}

throtl_init_add_tg_lists(td, tg, blkcg);
rcu_read_unlock();
return tg;
}
Expand Down Expand Up @@ -1014,6 +1080,15 @@ int blk_throtl_bio(struct request_queue *q, struct bio **biop)
spin_lock_irq(q->queue_lock);
tg = throtl_get_tg(td);

if (IS_ERR(tg)) {
if (PTR_ERR(tg) == -ENODEV) {
/*
* Queue is gone. No queue lock held here.
*/
return -ENODEV;
}
}

if (tg->nr_queued[rw]) {
/*
* There is already another bio queued in same dir. No
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128 changes: 95 additions & 33 deletions block/cfq-iosched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1016,28 +1016,47 @@ void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
cfqg->needs_update = true;
}

static struct cfq_group * cfq_find_alloc_cfqg(struct cfq_data *cfqd,
struct blkio_cgroup *blkcg)
static void cfq_init_add_cfqg_lists(struct cfq_data *cfqd,
struct cfq_group *cfqg, struct blkio_cgroup *blkcg)
{
struct cfq_group *cfqg = NULL;
void *key = cfqd;
int i, j;
struct cfq_rb_root *st;
struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
unsigned int major, minor;

cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
/*
* Add group onto cgroup list. It might happen that bdi->dev is
* not initialized yet. Initialize this new group without major
* and minor info and this info will be filled in once a new thread
* comes for IO.
*/
if (bdi->dev) {
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
cfqg->blkg.dev = MKDEV(major, minor);
goto done;
}
if (cfqg)
goto done;
cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
(void *)cfqd, MKDEV(major, minor));
} else
cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
(void *)cfqd, 0);

cfqd->nr_blkcg_linked_grps++;
cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);

/* Add group on cfqd list */
hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
}

/*
* Should be called from sleepable context. No request queue lock as per
* cpu stats are allocated dynamically and alloc_percpu needs to be called
* from sleepable context.
*/
static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
{
struct cfq_group *cfqg = NULL;
int i, j;
struct cfq_rb_root *st;

cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
if (!cfqg)
goto done;
return NULL;

for_each_cfqg_st(cfqg, i, j, st)
*st = CFQ_RB_ROOT;
Expand All @@ -1050,28 +1069,31 @@ static struct cfq_group * cfq_find_alloc_cfqg(struct cfq_data *cfqd,
* or cgroup deletion path depending on who is exiting first.
*/
cfqg->ref = 1;
return cfqg;
}

static struct cfq_group *
cfq_find_cfqg(struct cfq_data *cfqd, struct blkio_cgroup *blkcg)
{
struct cfq_group *cfqg = NULL;
void *key = cfqd;
struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
unsigned int major, minor;

/*
* Add group onto cgroup list. It might happen that bdi->dev is
* not initialized yet. Initialize this new group without major
* and minor info and this info will be filled in once a new thread
* comes for IO. See code above.
* This is the common case when there are no blkio cgroups.
* Avoid lookup in this case
*/
if (bdi->dev) {
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd,
MKDEV(major, minor));
} else
cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd,
0);

cfqd->nr_blkcg_linked_grps++;
cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);
if (blkcg == &blkio_root_cgroup)
cfqg = &cfqd->root_group;
else
cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));

/* Add group on cfqd list */
hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
cfqg->blkg.dev = MKDEV(major, minor);
}

done:
return cfqg;
}

Expand All @@ -1082,13 +1104,53 @@ static struct cfq_group * cfq_find_alloc_cfqg(struct cfq_data *cfqd,
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)
{
struct blkio_cgroup *blkcg;
struct cfq_group *cfqg = NULL;
struct cfq_group *cfqg = NULL, *__cfqg = NULL;
struct request_queue *q = cfqd->queue;

rcu_read_lock();
blkcg = task_blkio_cgroup(current);
cfqg = cfq_find_cfqg(cfqd, blkcg);
if (cfqg) {
rcu_read_unlock();
return cfqg;
}

/*
* Need to allocate a group. Allocation of group also needs allocation
* of per cpu stats which in-turn takes a mutex() and can block. Hence
* we need to drop rcu lock and queue_lock before we call alloc.
*
* Not taking any queue reference here and assuming that queue is
* around by the time we return. CFQ queue allocation code does
* the same. It might be racy though.
*/

rcu_read_unlock();
spin_unlock_irq(q->queue_lock);

cfqg = cfq_alloc_cfqg(cfqd);

spin_lock_irq(q->queue_lock);

rcu_read_lock();
blkcg = task_blkio_cgroup(current);
cfqg = cfq_find_alloc_cfqg(cfqd, blkcg);

/*
* If some other thread already allocated the group while we were
* not holding queue lock, free up the group
*/
__cfqg = cfq_find_cfqg(cfqd, blkcg);

if (__cfqg) {
kfree(cfqg);
rcu_read_unlock();
return __cfqg;
}

if (!cfqg)
cfqg = &cfqd->root_group;

cfq_init_add_cfqg_lists(cfqd, cfqg, blkcg);
rcu_read_unlock();
return cfqg;
}
Expand Down

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