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Commit bca4b914 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Jens Axboe
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cfq-iosched: remove dead_key from cfq_io_context 



Remove ->dead_key field from cfq_io_context to shrink its size to 128 bytes.
(64 bytes for 32-bit hosts)

Use lower bit in ->key as dead-mark, instead of moving key to separate field.
After this for dead cfq_io_context we got cic->key != cfqd automatically.
Thus, io_context's last-hit cache should work without changing.

Now to check ->key for non-dead state compare it with cfqd,
instead of checking ->key for non-null value as it was before.

Plus remove obsolete race protection in cfq_cic_lookup.
This race gone after v2.6.24-1728-g4ac845a

Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent f4b87dee

block/cfq-iosched.c

+28 −13
Original line number Diff line number Diff line
@@ -430,6 +430,23 @@ static inline void cic_set_cfqq(struct cfq_io_context *cic, 
	cic->cfqq[is_sync] = cfqq;

}



#define CIC_DEAD_KEY	1ul



static inline void *cfqd_dead_key(struct cfq_data *cfqd)

{

	return (void *)((unsigned long) cfqd | CIC_DEAD_KEY);

}



static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)

{

	struct cfq_data *cfqd = cic->key;



	if (unlikely((unsigned long) cfqd & CIC_DEAD_KEY))

		return NULL;



	return cfqd;

}



/*

 * We regard a request as SYNC, if it's either a read or has the SYNC bit

 * set (in which case it could also be direct WRITE).
@@ -2510,11 +2527,12 @@ static void cfq_cic_free(struct cfq_io_context *cic) 
static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)

{

	unsigned long flags;

	unsigned long dead_key = (unsigned long) cic->key;



	BUG_ON(!cic->dead_key);

	BUG_ON(!(dead_key & CIC_DEAD_KEY));



	spin_lock_irqsave(&ioc->lock, flags);

	radix_tree_delete(&ioc->radix_root, cic->dead_key);

	radix_tree_delete(&ioc->radix_root, dead_key & ~CIC_DEAD_KEY);

	hlist_del_rcu(&cic->cic_list);

	spin_unlock_irqrestore(&ioc->lock, flags);
@@ -2573,11 +2591,10 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd, 
	list_del_init(&cic->queue_list);



	/*

	 * Make sure key == NULL is seen for dead queues

	 * Make sure dead mark is seen for dead queues

	 */

	smp_wmb();

	cic->dead_key = (unsigned long) cic->key;

	cic->key = NULL;

	cic->key = cfqd_dead_key(cfqd);



	if (ioc->ioc_data == cic)

		rcu_assign_pointer(ioc->ioc_data, NULL);
@@ -2596,7 +2613,7 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd, 
static void cfq_exit_single_io_context(struct io_context *ioc,

				       struct cfq_io_context *cic)

{

	struct cfq_data *cfqd = cic->key;

	struct cfq_data *cfqd = cic_to_cfqd(cic);



	if (cfqd) {

		struct request_queue *q = cfqd->queue;
@@ -2609,7 +2626,7 @@ static void cfq_exit_single_io_context(struct io_context *ioc, 
		 * race between exiting task and queue

		 */

		smp_read_barrier_depends();

		if (cic->key)

		if (cic->key == cfqd)

			__cfq_exit_single_io_context(cfqd, cic);



		spin_unlock_irqrestore(q->queue_lock, flags);
@@ -2689,7 +2706,7 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc) 


static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)

{

	struct cfq_data *cfqd = cic->key;

	struct cfq_data *cfqd = cic_to_cfqd(cic);

	struct cfq_queue *cfqq;

	unsigned long flags;
@@ -2746,7 +2763,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)

{

	struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);

	struct cfq_data *cfqd = cic->key;

	struct cfq_data *cfqd = cic_to_cfqd(cic);

	unsigned long flags;

	struct request_queue *q;
@@ -2883,6 +2900,7 @@ cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc, 
	unsigned long flags;



	WARN_ON(!list_empty(&cic->queue_list));

	BUG_ON(cic->key != cfqd_dead_key(cfqd));



	spin_lock_irqsave(&ioc->lock, flags);
@@ -2900,7 +2918,6 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc) 
{

	struct cfq_io_context *cic;

	unsigned long flags;

	void *k;



	if (unlikely(!ioc))

		return NULL;
@@ -2921,9 +2938,7 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc) 
		rcu_read_unlock();

		if (!cic)

			break;

		/* ->key must be copied to avoid race with cfq_exit_queue() */

		k = cic->key;

		if (unlikely(!k)) {

		if (unlikely(cic->key != cfqd)) {

			cfq_drop_dead_cic(cfqd, ioc, cic);

			rcu_read_lock();

			continue;

include/linux/iocontext.h

+0 −1
Original line number Diff line number Diff line
@@ -7,7 +7,6 @@ 
struct cfq_queue;

struct cfq_io_context {

	void *key;

	unsigned long dead_key;



	struct cfq_queue *cfqq[2];