blkio: Take care of cgroup deletion and cfq group reference counting

o One can choose to change elevator or delete a cgroup. Implement group
  reference counting so that both elevator exit and cgroup deletion can
  take place gracefully.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Nauman Rafique <nauman@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Vivek Goyal 2009-12-03 12:59:47 -05:00 committed by Jens Axboe
parent 25fb5169d4
commit b1c3576961
3 changed files with 160 additions and 2 deletions

View file

@ -13,6 +13,8 @@
#include <linux/ioprio.h> #include <linux/ioprio.h>
#include "blk-cgroup.h" #include "blk-cgroup.h"
extern void cfq_unlink_blkio_group(void *, struct blkio_group *);
struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT }; struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup) struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
@ -28,14 +30,43 @@ void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
spin_lock_irqsave(&blkcg->lock, flags); spin_lock_irqsave(&blkcg->lock, flags);
rcu_assign_pointer(blkg->key, key); rcu_assign_pointer(blkg->key, key);
blkg->blkcg_id = css_id(&blkcg->css);
hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list); hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
spin_unlock_irqrestore(&blkcg->lock, flags); spin_unlock_irqrestore(&blkcg->lock, flags);
} }
static void __blkiocg_del_blkio_group(struct blkio_group *blkg)
{
hlist_del_init_rcu(&blkg->blkcg_node);
blkg->blkcg_id = 0;
}
/*
* returns 0 if blkio_group was still on cgroup list. Otherwise returns 1
* indicating that blk_group was unhashed by the time we got to it.
*/
int blkiocg_del_blkio_group(struct blkio_group *blkg) int blkiocg_del_blkio_group(struct blkio_group *blkg)
{ {
/* Implemented later */ struct blkio_cgroup *blkcg;
return 0; unsigned long flags;
struct cgroup_subsys_state *css;
int ret = 1;
rcu_read_lock();
css = css_lookup(&blkio_subsys, blkg->blkcg_id);
if (!css)
goto out;
blkcg = container_of(css, struct blkio_cgroup, css);
spin_lock_irqsave(&blkcg->lock, flags);
if (!hlist_unhashed(&blkg->blkcg_node)) {
__blkiocg_del_blkio_group(blkg);
ret = 0;
}
spin_unlock_irqrestore(&blkcg->lock, flags);
out:
rcu_read_unlock();
return ret;
} }
/* called under rcu_read_lock(). */ /* called under rcu_read_lock(). */
@ -97,8 +128,39 @@ static int blkiocg_populate(struct cgroup_subsys *subsys, struct cgroup *cgroup)
static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup) static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)
{ {
struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup); struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
unsigned long flags;
struct blkio_group *blkg;
void *key;
rcu_read_lock();
remove_entry:
spin_lock_irqsave(&blkcg->lock, flags);
if (hlist_empty(&blkcg->blkg_list)) {
spin_unlock_irqrestore(&blkcg->lock, flags);
goto done;
}
blkg = hlist_entry(blkcg->blkg_list.first, struct blkio_group,
blkcg_node);
key = rcu_dereference(blkg->key);
__blkiocg_del_blkio_group(blkg);
spin_unlock_irqrestore(&blkcg->lock, flags);
/*
* This blkio_group is being unlinked as associated cgroup is going
* away. Let all the IO controlling policies know about this event.
*
* Currently this is static call to one io controlling policy. Once
* we have more policies in place, we need some dynamic registration
* of callback function.
*/
cfq_unlink_blkio_group(key, blkg);
goto remove_entry;
done:
free_css_id(&blkio_subsys, &blkcg->css); free_css_id(&blkio_subsys, &blkcg->css);
rcu_read_unlock();
kfree(blkcg); kfree(blkcg);
} }

View file

@ -26,6 +26,7 @@ struct blkio_group {
/* An rcu protected unique identifier for the group */ /* An rcu protected unique identifier for the group */
void *key; void *key;
struct hlist_node blkcg_node; struct hlist_node blkcg_node;
unsigned short blkcg_id;
}; };
#define BLKIO_WEIGHT_MIN 100 #define BLKIO_WEIGHT_MIN 100

View file

@ -192,6 +192,7 @@ struct cfq_group {
struct blkio_group blkg; struct blkio_group blkg;
#ifdef CONFIG_CFQ_GROUP_IOSCHED #ifdef CONFIG_CFQ_GROUP_IOSCHED
struct hlist_node cfqd_node; struct hlist_node cfqd_node;
atomic_t ref;
#endif #endif
}; };
@ -924,6 +925,14 @@ cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
*st = CFQ_RB_ROOT; *st = CFQ_RB_ROOT;
RB_CLEAR_NODE(&cfqg->rb_node); RB_CLEAR_NODE(&cfqg->rb_node);
/*
* Take the initial reference that will be released on destroy
* This can be thought of a joint reference by cgroup and
* elevator which will be dropped by either elevator exit
* or cgroup deletion path depending on who is exiting first.
*/
atomic_set(&cfqg->ref, 1);
/* Add group onto cgroup list */ /* Add group onto cgroup list */
blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd); blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd);
@ -960,7 +969,77 @@ static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
cfqg = &cfqq->cfqd->root_group; cfqg = &cfqq->cfqd->root_group;
cfqq->cfqg = cfqg; cfqq->cfqg = cfqg;
/* cfqq reference on cfqg */
atomic_inc(&cfqq->cfqg->ref);
} }
static void cfq_put_cfqg(struct cfq_group *cfqg)
{
struct cfq_rb_root *st;
int i, j;
BUG_ON(atomic_read(&cfqg->ref) <= 0);
if (!atomic_dec_and_test(&cfqg->ref))
return;
for_each_cfqg_st(cfqg, i, j, st)
BUG_ON(!RB_EMPTY_ROOT(&st->rb) || st->active != NULL);
kfree(cfqg);
}
static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
/* Something wrong if we are trying to remove same group twice */
BUG_ON(hlist_unhashed(&cfqg->cfqd_node));
hlist_del_init(&cfqg->cfqd_node);
/*
* Put the reference taken at the time of creation so that when all
* queues are gone, group can be destroyed.
*/
cfq_put_cfqg(cfqg);
}
static void cfq_release_cfq_groups(struct cfq_data *cfqd)
{
struct hlist_node *pos, *n;
struct cfq_group *cfqg;
hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
/*
* If cgroup removal path got to blk_group first and removed
* it from cgroup list, then it will take care of destroying
* cfqg also.
*/
if (!blkiocg_del_blkio_group(&cfqg->blkg))
cfq_destroy_cfqg(cfqd, cfqg);
}
}
/*
* Blk cgroup controller notification saying that blkio_group object is being
* delinked as associated cgroup object is going away. That also means that
* no new IO will come in this group. So get rid of this group as soon as
* any pending IO in the group is finished.
*
* This function is called under rcu_read_lock(). key is the rcu protected
* pointer. That means "key" is a valid cfq_data pointer as long as we are rcu
* read lock.
*
* "key" was fetched from blkio_group under blkio_cgroup->lock. That means
* it should not be NULL as even if elevator was exiting, cgroup deltion
* path got to it first.
*/
void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg)
{
unsigned long flags;
struct cfq_data *cfqd = key;
spin_lock_irqsave(cfqd->queue->queue_lock, flags);
cfq_destroy_cfqg(cfqd, cfqg_of_blkg(blkg));
spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}
#else /* GROUP_IOSCHED */ #else /* GROUP_IOSCHED */
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create) static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
{ {
@ -971,6 +1050,9 @@ cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
cfqq->cfqg = cfqg; cfqq->cfqg = cfqg;
} }
static void cfq_release_cfq_groups(struct cfq_data *cfqd) {}
static inline void cfq_put_cfqg(struct cfq_group *cfqg) {}
#endif /* GROUP_IOSCHED */ #endif /* GROUP_IOSCHED */
/* /*
@ -2172,11 +2254,13 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
* task holds one reference to the queue, dropped when task exits. each rq * task holds one reference to the queue, dropped when task exits. each rq
* in-flight on this queue also holds a reference, dropped when rq is freed. * in-flight on this queue also holds a reference, dropped when rq is freed.
* *
* Each cfq queue took a reference on the parent group. Drop it now.
* queue lock must be held here. * queue lock must be held here.
*/ */
static void cfq_put_queue(struct cfq_queue *cfqq) static void cfq_put_queue(struct cfq_queue *cfqq)
{ {
struct cfq_data *cfqd = cfqq->cfqd; struct cfq_data *cfqd = cfqq->cfqd;
struct cfq_group *cfqg;
BUG_ON(atomic_read(&cfqq->ref) <= 0); BUG_ON(atomic_read(&cfqq->ref) <= 0);
@ -2186,6 +2270,7 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
cfq_log_cfqq(cfqd, cfqq, "put_queue"); cfq_log_cfqq(cfqd, cfqq, "put_queue");
BUG_ON(rb_first(&cfqq->sort_list)); BUG_ON(rb_first(&cfqq->sort_list));
BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]); BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
cfqg = cfqq->cfqg;
if (unlikely(cfqd->active_queue == cfqq)) { if (unlikely(cfqd->active_queue == cfqq)) {
__cfq_slice_expired(cfqd, cfqq, 0); __cfq_slice_expired(cfqd, cfqq, 0);
@ -2194,6 +2279,7 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
BUG_ON(cfq_cfqq_on_rr(cfqq)); BUG_ON(cfq_cfqq_on_rr(cfqq));
kmem_cache_free(cfq_pool, cfqq); kmem_cache_free(cfq_pool, cfqq);
cfq_put_cfqg(cfqg);
} }
/* /*
@ -3369,11 +3455,15 @@ static void cfq_exit_queue(struct elevator_queue *e)
} }
cfq_put_async_queues(cfqd); cfq_put_async_queues(cfqd);
cfq_release_cfq_groups(cfqd);
blkiocg_del_blkio_group(&cfqd->root_group.blkg);
spin_unlock_irq(q->queue_lock); spin_unlock_irq(q->queue_lock);
cfq_shutdown_timer_wq(cfqd); cfq_shutdown_timer_wq(cfqd);
/* Wait for cfqg->blkg->key accessors to exit their grace periods. */
synchronize_rcu();
kfree(cfqd); kfree(cfqd);
} }
@ -3401,6 +3491,11 @@ static void *cfq_init_queue(struct request_queue *q)
cfqg->weight = 2*BLKIO_WEIGHT_DEFAULT; cfqg->weight = 2*BLKIO_WEIGHT_DEFAULT;
#ifdef CONFIG_CFQ_GROUP_IOSCHED #ifdef CONFIG_CFQ_GROUP_IOSCHED
/*
* Take a reference to root group which we never drop. This is just
* to make sure that cfq_put_cfqg() does not try to kfree root group
*/
atomic_set(&cfqg->ref, 1);
blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg, (void *)cfqd); blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg, (void *)cfqd);
#endif #endif
/* /*