Messages in this thread Patch in this message | | | Date | Wed, 7 Mar 2012 14:13:34 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCHSET] mempool, percpu, blkcg: fix percpu stat allocation and remove stats_lock |
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On Wed, Mar 07, 2012 at 09:05:44AM -0800, Tejun Heo wrote:
[..] > > +alloc_stats: > > + spin_lock_irq(&alloc_list_lock); > > + if (list_empty(&alloc_list)) { > > + /* No more groups needing per cpu stat allocation */ > > + spin_unlock_irq(&alloc_list_lock); > > + return; > > + } > > + spin_unlock_irq(&alloc_list_lock); > > I don't think we really need the above. Just proceed with allocation.
Hi Tejun,
Here is V4 of the patch which takes care of your suggestions.
Thanks Vivek
blk-cgroup: Alloc per cpu stats from worker thread in a delayed manner
Current per cpu stat allocation assumes GFP_KERNEL allocation flag. But in IO path there are times when we want GFP_NOIO semantics. As there is no way to pass the allocation flags to alloc_percpu(), this patch delays the allocation of stats using a worker thread.
v2-> tejun suggested following changes. Changed the patch accordingly. - move alloc_node location in structure - reduce the size of names of some of the fields - Reduce the scope of locking of alloc_list_lock - Simplified stat_alloc_fn() by allocating stats for all policies in one go and then assigning these to a group.
v3 -> Andrew suggested to put some comments in the code. Also raised concerns about trying to allocate infinitely in case of allocation failure. I have changed the logic to sleep for 10ms before retrying. That should take care of non-preemptible UP kernels.
v4 -> Tejun had more suggestions. - drop list_for_each_entry_all() - instead of msleep() use queue_delayed_work() - Some cleanups realted to more compact coding.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com> --- block/blk-cgroup.c | 136 +++++++++++++++++++++++++++++++++++++---------------- block/blk-cgroup.h | 2 2 files changed, 98 insertions(+), 40 deletions(-)
Index: tejun-misc/block/blk-cgroup.c =================================================================== --- tejun-misc.orig/block/blk-cgroup.c 2012-03-07 20:36:44.019949136 -0500 +++ tejun-misc/block/blk-cgroup.c 2012-03-08 00:56:03.374961752 -0500 @@ -30,6 +30,15 @@ static LIST_HEAD(blkio_list); static DEFINE_MUTEX(all_q_mutex); static LIST_HEAD(all_q_list); +/* List of groups pending per cpu stats allocation */ +static DEFINE_SPINLOCK(alloc_list_lock); +static LIST_HEAD(alloc_list); + +/* Array of per cpu stat pointers allocated for blk groups */ +static void *pcpu_stats[BLKIO_NR_POLICIES]; +static void blkio_stat_alloc_fn(struct work_struct *); +static DECLARE_DELAYED_WORK(blkio_stat_alloc_work, blkio_stat_alloc_fn); + struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT }; EXPORT_SYMBOL_GPL(blkio_root_cgroup); @@ -391,6 +400,10 @@ void blkiocg_update_dispatch_stats(struc struct blkio_group_stats_cpu *stats_cpu; unsigned long flags; + /* If per cpu stats are not allocated yet, don't do any accounting. */ + if (pd->stats_cpu == NULL) + return; + /* * Disabling interrupts to provide mutual exclusion between two * writes on same cpu. It probably is not needed for 64bit. Not @@ -443,6 +456,10 @@ void blkiocg_update_io_merged_stats(stru struct blkio_group_stats_cpu *stats_cpu; unsigned long flags; + /* If per cpu stats are not allocated yet, don't do any accounting. */ + if (pd->stats_cpu == NULL) + return; + /* * Disabling interrupts to provide mutual exclusion between two * writes on same cpu. It probably is not needed for 64bit. Not @@ -460,6 +477,65 @@ void blkiocg_update_io_merged_stats(stru } EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats); +/* + * Worker for allocating per cpu stat for blk groups. This is scheduled + * once there are some groups on the alloc_list waiting for allocation + */ +static void blkio_stat_alloc_fn(struct work_struct *work) +{ + + struct delayed_work *dwork = to_delayed_work(work); + struct blkio_group *blkg; + int i; + bool alloc_more = false; + +alloc_stats: + for (i = 0; i < BLKIO_NR_POLICIES; i++) { + if (pcpu_stats[i] != NULL) + continue; + + pcpu_stats[i] = alloc_percpu(struct blkio_group_stats_cpu); + + /* Allocation failed. Try again after some time. */ + if (pcpu_stats[i] == NULL) { + queue_delayed_work(system_nrt_wq, dwork, + msecs_to_jiffies(10)); + return; + } + } + + spin_lock_irq(&blkio_list_lock); + spin_lock(&alloc_list_lock); + + /* cgroup got deleted or queue exited. */ + if (list_empty(&alloc_list)) { + alloc_more = false; + goto unlock; + } + + blkg = list_first_entry(&alloc_list, struct blkio_group, alloc_node); + + for (i = 0; i < BLKIO_NR_POLICIES; i++) { + struct blkg_policy_data *pd = blkg->pd[i]; + + if (blkio_policy[i] && pd && !pd->stats_cpu) + swap(pd->stats_cpu, pcpu_stats[i]); + } + + list_del_init(&blkg->alloc_node); + + if (list_empty(&alloc_list)) + alloc_more = false; + else + alloc_more = true; +unlock: + spin_unlock(&alloc_list_lock); + spin_unlock_irq(&blkio_list_lock); + + if (alloc_more) + goto alloc_stats; +} + /** * blkg_free - free a blkg * @blkg: blkg to free @@ -491,9 +567,6 @@ static void blkg_free(struct blkio_group * @q: request_queue the new blkg is associated with * * Allocate a new blkg assocating @blkcg and @q. - * - * FIXME: Should be called with queue locked but currently isn't due to - * percpu stat breakage. */ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg, struct request_queue *q) @@ -509,6 +582,7 @@ static struct blkio_group *blkg_alloc(st spin_lock_init(&blkg->stats_lock); blkg->q = q; INIT_LIST_HEAD(&blkg->q_node); + INIT_LIST_HEAD(&blkg->alloc_node); blkg->blkcg = blkcg; blkg->refcnt = 1; cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path)); @@ -530,13 +604,6 @@ static struct blkio_group *blkg_alloc(st blkg->pd[i] = pd; pd->blkg = blkg; - - /* broken, read comment in the callsite */ - pd->stats_cpu = alloc_percpu(struct blkio_group_stats_cpu); - if (!pd->stats_cpu) { - blkg_free(blkg); - return NULL; - } } /* invoke per-policy init */ @@ -556,7 +623,7 @@ struct blkio_group *blkg_lookup_create(s bool for_root) __releases(q->queue_lock) __acquires(q->queue_lock) { - struct blkio_group *blkg, *new_blkg; + struct blkio_group *blkg; WARN_ON_ONCE(!rcu_read_lock_held()); lockdep_assert_held(q->queue_lock); @@ -580,48 +647,27 @@ struct blkio_group *blkg_lookup_create(s /* * Allocate and initialize. - * - * FIXME: The following is broken. Percpu memory allocation - * requires %GFP_KERNEL context and can't be performed from IO - * path. Allocation here should inherently be atomic and the - * following lock dancing can be removed once the broken percpu - * allocation is fixed. */ - spin_unlock_irq(q->queue_lock); - rcu_read_unlock(); - - new_blkg = blkg_alloc(blkcg, q); - - rcu_read_lock(); - spin_lock_irq(q->queue_lock); - - /* did bypass get turned on inbetween? */ - if (unlikely(blk_queue_bypass(q)) && !for_root) { - blkg = ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY); - goto out; - } - - /* did someone beat us to it? */ - blkg = blkg_lookup(blkcg, q); - if (unlikely(blkg)) - goto out; + blkg = blkg_alloc(blkcg, q); /* did alloc fail? */ - if (unlikely(!new_blkg)) { + if (unlikely(!blkg)) { blkg = ERR_PTR(-ENOMEM); goto out; } /* insert */ spin_lock(&blkcg->lock); - swap(blkg, new_blkg); - hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list); list_add(&blkg->q_node, &q->blkg_list); - spin_unlock(&blkcg->lock); + + spin_lock(&alloc_list_lock); + list_add(&blkg->alloc_node, &alloc_list); + /* Queue per cpu stat allocation from worker thread. */ + queue_delayed_work(system_nrt_wq, &blkio_stat_alloc_work, 0); + spin_unlock(&alloc_list_lock); out: - blkg_free(new_blkg); return blkg; } EXPORT_SYMBOL_GPL(blkg_lookup_create); @@ -654,6 +700,10 @@ static void blkg_destroy(struct blkio_gr list_del_init(&blkg->q_node); hlist_del_init_rcu(&blkg->blkcg_node); + spin_lock(&alloc_list_lock); + list_del_init(&blkg->alloc_node); + spin_unlock(&alloc_list_lock); + /* * Put the reference taken at the time of creation so that when all * queues are gone, group can be destroyed. @@ -752,6 +802,9 @@ static void blkio_reset_stats_cpu(struct struct blkg_policy_data *pd = blkg->pd[plid]; struct blkio_group_stats_cpu *stats_cpu; int i, j, k; + + if (pd->stats_cpu == NULL) + return; /* * Note: On 64 bit arch this should not be an issue. This has the * possibility of returning some inconsistent value on 32bit arch @@ -883,6 +936,9 @@ static uint64_t blkio_read_stat_cpu(stru struct blkio_group_stats_cpu *stats_cpu; u64 val = 0, tval; + if (pd->stats_cpu == NULL) + return val; + for_each_possible_cpu(cpu) { unsigned int start; stats_cpu = per_cpu_ptr(pd->stats_cpu, cpu); Index: tejun-misc/block/blk-cgroup.h =================================================================== --- tejun-misc.orig/block/blk-cgroup.h 2012-03-07 20:36:44.007949131 -0500 +++ tejun-misc/block/blk-cgroup.h 2012-03-07 20:37:51.189951195 -0500 @@ -190,6 +190,8 @@ struct blkio_group { spinlock_t stats_lock; struct blkg_policy_data *pd[BLKIO_NR_POLICIES]; + /* List of blkg waiting for per cpu stats memory to be allocated */ + struct list_head alloc_node; struct rcu_head rcu_head; };
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