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Date: Thu, 20 May 2010 23:21:34 +0400
From: Konstantin Khlebnikov <khlebnikov@...nvz.org>
To: <linux-kernel@...r.kernel.org>, Jens Axboe <jens.axboe@...cle.com>
CC: Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH 1/2] 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: Konstantin Khlebnikov <khlebnikov@...nvz.org>
---
block/cfq-iosched.c | 41 ++++++++++++++++++++++++++++-------------
include/linux/iocontext.h | 1 -
2 files changed, 28 insertions(+), 14 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5f127cf..67745e5 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -431,6 +431,23 @@ 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).
@@ -2476,11 +2493,12 @@ 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);
@@ -2539,11 +2557,10 @@ 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);
@@ -2562,7 +2579,7 @@ 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;
@@ -2575,7 +2592,7 @@ 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);
@@ -2655,7 +2672,7 @@ 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;
@@ -2712,7 +2729,7 @@ 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;
@@ -2849,6 +2866,7 @@ 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);
@@ -2866,7 +2884,6 @@ 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;
@@ -2887,9 +2904,7 @@ 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;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index a0bb301..64d5291 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -7,7 +7,6 @@
struct cfq_queue;
struct cfq_io_context {
void *key;
- unsigned long dead_key;
struct cfq_queue *cfqq[2];
--
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