raid5: relieve lock contention in get_active_stripe()

track empty inactive list count, so md_raid5_congested() can use it to make
decision.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 8 insertions, 1 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 93090b2afab4..1fb28c56457a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -356,6 +356,9 @@ static void release_inactive_stripe_list(struct r5conf *conf,
                  */
                 if (!list_empty_careful(list)) {
                         spin_lock_irqsave(conf->hash_locks + hash, flags);
+                        if (list_empty(conf->inactive_list + hash) &&
+                            !list_empty(list))
+                                atomic_dec(&conf->empty_inactive_list_nr);
                         list_splice_tail_init(list, conf->inactive_list + hash);
                         do_wakeup = true;
                         spin_unlock_irqrestore(conf->hash_locks + hash, flags);
@@ -477,6 +480,8 @@ static struct stripe_head *get_free_stripe(struct r5conf *conf, int hash)
         remove_hash(sh);
         atomic_inc(&conf->active_stripes);
         BUG_ON(hash != sh->hash_lock_index);
+        if (list_empty(conf->inactive_list + hash))
+                atomic_inc(&conf->empty_inactive_list_nr);
 out:
         return sh;
 }
@@ -4059,7 +4064,7 @@ int md_raid5_congested(struct mddev *mddev, int bits)
                 return 1;
         if (conf->quiesce)
                 return 1;
-        if (atomic_read(&conf->active_stripes) == conf->max_nr_stripes)
+        if (atomic_read(&conf->empty_inactive_list_nr))
                 return 1;
 
         return 0;
@@ -5750,6 +5755,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 
         memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
                  max_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
+        atomic_set(&conf->empty_inactive_list_nr, NR_STRIPE_HASH_LOCKS);
         if (grow_stripes(conf, NR_STRIPES)) {
                 printk(KERN_ERR
                        "md/raid:%s: couldn't allocate %dkB for buffers\n",
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index a9e443a1116f..e4407388670a 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -475,6 +475,7 @@ struct r5conf {
          */
         atomic_t                active_stripes;
         struct list_head        inactive_list[NR_STRIPE_HASH_LOCKS];
+        atomic_t                empty_inactive_list_nr;
         struct llist_head       released_stripes;
         wait_queue_head_t       wait_for_stripe;
         wait_queue_head_t       wait_for_overlap;