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Commit 4fb72036 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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blk-throttle: remove asynchrnous percpu stats allocation mechanism 



Because percpu allocator couldn't do non-blocking allocations,
blk-throttle was forced to implement an ad-hoc asynchronous allocation
mechanism for its percpu stats for cases where blkg's (blkcg_gq's) are
allocated from an IO path without sleepable context.

Now that percpu allocator can handle gfp_mask and blkg_policy_data
alloc / free are handled by policy methods, the ad-hoc asynchronous
allocation mechanism can be replaced with direct allocation from
tg_stats_alloc_fn().  Rit it out.

This ensures that an active throtl_grp always has valid non-NULL
->stats_cpu.  Remove checks on it.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 001bea73

block/blk-throttle.c

+25 −87
Original line number Diff line number Diff line
@@ -144,9 +144,6 @@ struct throtl_grp { 


	/* Per cpu stats pointer */

	struct tg_stats_cpu __percpu *stats_cpu;



	/* List of tgs waiting for per cpu stats memory to be allocated */

	struct list_head stats_alloc_node;

};



struct throtl_data
@@ -168,13 +165,6 @@ struct throtl_data 
	struct work_struct dispatch_work;

};



/* list and work item to allocate percpu group stats */

static DEFINE_SPINLOCK(tg_stats_alloc_lock);

static LIST_HEAD(tg_stats_alloc_list);



static void tg_stats_alloc_fn(struct work_struct *);

static DECLARE_DELAYED_WORK(tg_stats_alloc_work, tg_stats_alloc_fn);



static void throtl_pending_timer_fn(unsigned long arg);



static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
@@ -256,53 +246,6 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq) 
	}								\

} while (0)



static void tg_stats_init(struct tg_stats_cpu *tg_stats)

{

	blkg_rwstat_init(&tg_stats->service_bytes);

	blkg_rwstat_init(&tg_stats->serviced);

}



/*

 * Worker for allocating per cpu stat for tgs. This is scheduled on the

 * system_wq once there are some groups on the alloc_list waiting for

 * allocation.

 */

static void tg_stats_alloc_fn(struct work_struct *work)

{

	static struct tg_stats_cpu *stats_cpu;	/* this fn is non-reentrant */

	struct delayed_work *dwork = to_delayed_work(work);

	bool empty = false;



alloc_stats:

	if (!stats_cpu) {

		int cpu;



		stats_cpu = alloc_percpu(struct tg_stats_cpu);

		if (!stats_cpu) {

			/* allocation failed, try again after some time */

			schedule_delayed_work(dwork, msecs_to_jiffies(10));

			return;

		}

		for_each_possible_cpu(cpu)

			tg_stats_init(per_cpu_ptr(stats_cpu, cpu));

	}



	spin_lock_irq(&tg_stats_alloc_lock);



	if (!list_empty(&tg_stats_alloc_list)) {

		struct throtl_grp *tg = list_first_entry(&tg_stats_alloc_list,

							 struct throtl_grp,

							 stats_alloc_node);

		swap(tg->stats_cpu, stats_cpu);

		list_del_init(&tg->stats_alloc_node);

	}



	empty = list_empty(&tg_stats_alloc_list);

	spin_unlock_irq(&tg_stats_alloc_lock);

	if (!empty)

		goto alloc_stats;

}



static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)

{

	INIT_LIST_HEAD(&qn->node);
@@ -405,7 +348,27 @@ static void throtl_service_queue_exit(struct throtl_service_queue *sq) 


static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)

{

	return kzalloc_node(sizeof(struct throtl_grp), gfp, node);

	struct throtl_grp *tg;

	int cpu;



	tg = kzalloc_node(sizeof(*tg), gfp, node);

	if (!tg)

		return NULL;



	tg->stats_cpu = alloc_percpu_gfp(struct tg_stats_cpu, gfp);

	if (!tg->stats_cpu) {

		kfree(tg);

		return NULL;

	}



	for_each_possible_cpu(cpu) {

		struct tg_stats_cpu *stats_cpu = per_cpu_ptr(tg->stats_cpu, cpu);



		blkg_rwstat_init(&stats_cpu->service_bytes);

		blkg_rwstat_init(&stats_cpu->serviced);

	}



	return &tg->pd;

}



static void throtl_pd_init(struct blkcg_gq *blkg)
@@ -413,7 +376,6 @@ static void throtl_pd_init(struct blkcg_gq *blkg) 
	struct throtl_grp *tg = blkg_to_tg(blkg);

	struct throtl_data *td = blkg->q->td;

	struct throtl_service_queue *parent_sq;

	unsigned long flags;

	int rw;



	/*
@@ -448,16 +410,6 @@ static void throtl_pd_init(struct blkcg_gq *blkg) 
	tg->bps[WRITE] = -1;

	tg->iops[READ] = -1;

	tg->iops[WRITE] = -1;



	/*

	 * Ugh... We need to perform per-cpu allocation for tg->stats_cpu

	 * but percpu allocator can't be called from IO path.  Queue tg on

	 * tg_stats_alloc_list and allocate from work item.

	 */

	spin_lock_irqsave(&tg_stats_alloc_lock, flags);

	list_add(&tg->stats_alloc_node, &tg_stats_alloc_list);

	schedule_delayed_work(&tg_stats_alloc_work, 0);

	spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);

}



/*
@@ -487,20 +439,16 @@ static void throtl_pd_online(struct blkcg_gq *blkg) 
static void throtl_pd_exit(struct blkcg_gq *blkg)

{

	struct throtl_grp *tg = blkg_to_tg(blkg);

	unsigned long flags;



	spin_lock_irqsave(&tg_stats_alloc_lock, flags);

	list_del_init(&tg->stats_alloc_node);

	spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);



	free_percpu(tg->stats_cpu);



	throtl_service_queue_exit(&tg->service_queue);

}



static void throtl_pd_free(struct blkg_policy_data *pd)

{

	kfree(pd);

	struct throtl_grp *tg = pd_to_tg(pd);



	free_percpu(tg->stats_cpu);

	kfree(tg);

}



static void throtl_pd_reset_stats(struct blkcg_gq *blkg)
@@ -508,9 +456,6 @@ static void throtl_pd_reset_stats(struct blkcg_gq *blkg) 
	struct throtl_grp *tg = blkg_to_tg(blkg);

	int cpu;



	if (tg->stats_cpu == NULL)

		return;



	for_each_possible_cpu(cpu) {

		struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
@@ -973,10 +918,6 @@ static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes, 
	struct tg_stats_cpu *stats_cpu;

	unsigned long flags;



	/* If per cpu stats are not allocated yet, don't do any accounting. */

	if (tg->stats_cpu == NULL)

		return;



	/*

	 * Disabling interrupts to provide mutual exclusion between two

	 * writes on same cpu. It probably is not needed for 64bit. Not
@@ -1302,9 +1243,6 @@ static u64 tg_prfill_cpu_rwstat(struct seq_file *sf, 
	struct blkg_rwstat rwstat = { }, tmp;

	int i, cpu;



	if (tg->stats_cpu == NULL)

		return 0;



	for_each_possible_cpu(cpu) {

		struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);