From: Jeff Moyer <jmoyer@redhat.com>
Date: Thu, 25 Mar 2010 16:53:13 -0400
Subject: [block] cfq-iosched: fix async queue behaviour
Message-id: <1269535995-21213-4-git-send-email-jmoyer@redhat.com>
Patchwork-id: 23752
O-Subject: [RHEL5 PATCH 3/5] cfq-iosched: fix async queue behaviour
Bugzilla: 574285
RH-Acked-by: Josef Bacik <josef@redhat.com>
RH-Acked-by: Vivek Goyal <vgoyal@redhat.com>
RH-Acked-by: Jerome Marchand <jmarchan@redhat.com>

This is related to bug 574285.

commit 15c31be4d5bd2402c6f5a288d56a24edc9252b71
Author: Jens Axboe <jens.axboe@oracle.com>
Date:   Tue Jul 10 13:43:25 2007 +0200

    cfq-iosched: fix async queue behaviour

    With the cfq_queue hash removal, we inadvertently got rid of the
    async queue sharing. This was not intentional, in fact CFQ purposely
    shares the async queue per priority level to get good merging for
    async writes.

    So put some logic in cfq_get_queue() to track the shared queues.

    Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5fb1fc2..bcc8628 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -131,6 +131,8 @@ struct cfq_data {
 	int cur_prio, cur_end_prio;
 	unsigned int dispatch_slice;
 
+	struct cfq_queue *async_cfqq[IOPRIO_BE_NR];
+
 	struct timer_list idle_class_timer;
 
 	sector_t last_position;
@@ -1716,8 +1718,8 @@ static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
 }
 
 static struct cfq_queue *
-cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct task_struct *tsk,
-	      gfp_t gfp_mask)
+cfq_find_alloc_queue(struct cfq_data *cfqd, int is_sync,
+		     struct task_struct *tsk, gfp_t gfp_mask)
 {
 	struct cfq_queue *cfqq, *new_cfqq = NULL;
 	struct cfq_io_context *cic;
@@ -1765,12 +1767,35 @@ retry:
 	if (new_cfqq)
 		kmem_cache_free(cfq_pool, new_cfqq);
 
-	atomic_inc(&cfqq->ref);
 out:
 	WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
 	return cfqq;
 }
 
+static struct cfq_queue *
+cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct task_struct *tsk,
+	      gfp_t gfp_mask)
+{
+	const int ioprio = task_ioprio(tsk);
+	struct cfq_queue *cfqq = NULL;
+
+	if (!is_sync)
+		cfqq = cfqd->async_cfqq[ioprio];
+	if (!cfqq)
+		cfqq = cfq_find_alloc_queue(cfqd, is_sync, tsk, gfp_mask);
+
+	/*
+	 * pin the queue now that it's allocated, scheduler exit will prune it
+	 */
+	if (!is_sync && !cfqd->async_cfqq[ioprio]) {
+		atomic_inc(&cfqq->ref);
+		cfqd->async_cfqq[ioprio] = cfqq;
+	}
+
+	atomic_inc(&cfqq->ref);
+	return cfqq;
+}
+
 static void
 cfq_drop_dead_cic(struct io_context *ioc, struct cfq_io_context *cic)
 {
@@ -2546,6 +2571,7 @@ static void cfq_exit_queue(elevator_t *e)
 {
 	struct cfq_data *cfqd = e->elevator_data;
 	request_queue_t *q = cfqd->queue;
+	int i;
 
 	cfq_shutdown_timer_wq(cfqd);
 
@@ -2571,6 +2597,13 @@ static void cfq_exit_queue(elevator_t *e)
 		list_del_init(&cic->queue_list);
 	}
 
+	/*
+	 * Put the async queues
+	 */
+	for (i = 0; i < IOPRIO_BE_NR; i++)
+		if (cfqd->async_cfqq[i])	
+			cfq_put_queue(cfqd->async_cfqq[i]);
+
 	spin_unlock_irq(q->queue_lock);
 	spin_unlock(&cfq_exit_lock);
 
diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
index 63420f2..cb6722e 100644
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -47,8 +47,10 @@ enum {
 #define IOPRIO_NORM	(4)
 static inline int task_ioprio(struct task_struct *task)
 {
-	WARN_ON(!ioprio_valid(task->ioprio));
-	return IOPRIO_PRIO_DATA(task->ioprio);
+	if (ioprio_valid(task->ioprio))
+		return IOPRIO_PRIO_DATA(task->ioprio);
+
+	return IOPRIO_NORM;
 }
 
 static inline int task_nice_ioprio(struct task_struct *task)