raid5: make_request use batch stripe release

make_request() does stripe release for every stripe and the stripe usually has
count 1, which makes previous release_stripe() optimization not work. In my
test, this release_stripe() becomes the heaviest pleace to take
conf->device_lock after previous patches applied.

Below patch makes stripe release batch. All the stripes will be released in
unplug. The STRIPE_ON_UNPLUG_LIST bit is to protect concurrent access stripe
lru.

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

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bde9da2baa392d76a1ea885a136790487ccf962f..978ba9b7a3c4d6019ce1a550009e5a4e108ab152 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -471,7 +471,8 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
                } else {
                        if (atomic_read(&sh->count)) {
                                BUG_ON(!list_empty(&sh->lru)
-                                   && !test_bit(STRIPE_EXPANDING, &sh->state));
+                                   && !test_bit(STRIPE_EXPANDING, &sh->state)
+                                   && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state));
                        } else {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
@@ -3988,6 +3989,62 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf)
        return sh;
 }
 
+struct raid5_plug_cb {
+       struct blk_plug_cb      cb;
+       struct list_head        list;
+};
+
+static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
+{
+       struct raid5_plug_cb *cb = container_of(
+               blk_cb, struct raid5_plug_cb, cb);
+       struct stripe_head *sh;
+       struct mddev *mddev = cb->cb.data;
+       struct r5conf *conf = mddev->private;
+
+       if (cb->list.next && !list_empty(&cb->list)) {
+               spin_lock_irq(&conf->device_lock);
+               while (!list_empty(&cb->list)) {
+                       sh = list_first_entry(&cb->list, struct stripe_head, lru);
+                       list_del_init(&sh->lru);
+                       /*
+                        * avoid race release_stripe_plug() sees
+                        * STRIPE_ON_UNPLUG_LIST clear but the stripe
+                        * is still in our list
+                        */
+                       smp_mb__before_clear_bit();
+                       clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
+                       __release_stripe(conf, sh);
+               }
+               spin_unlock_irq(&conf->device_lock);
+       }
+       kfree(cb);
+}
+
+static void release_stripe_plug(struct mddev *mddev,
+                               struct stripe_head *sh)
+{
+       struct blk_plug_cb *blk_cb = blk_check_plugged(
+               raid5_unplug, mddev,
+               sizeof(struct raid5_plug_cb));
+       struct raid5_plug_cb *cb;
+
+       if (!blk_cb) {
+               release_stripe(sh);
+               return;
+       }
+
+       cb = container_of(blk_cb, struct raid5_plug_cb, cb);
+
+       if (cb->list.next == NULL)
+               INIT_LIST_HEAD(&cb->list);
+
+       if (!test_and_set_bit(STRIPE_ON_UNPLUG_LIST, &sh->state))
+               list_add_tail(&sh->lru, &cb->list);
+       else
+               release_stripe(sh);
+}
+
 static void make_request(struct mddev *mddev, struct bio * bi)
 {
        struct r5conf *conf = mddev->private;
@@ -4116,8 +4173,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                        if ((bi->bi_rw & REQ_SYNC) &&
                            !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                                atomic_inc(&conf->preread_active_stripes);
-                       mddev_check_plugged(mddev);
-                       release_stripe(sh);
+                       release_stripe_plug(mddev, sh);
                } else {
                        /* cannot get stripe for read-ahead, just give-up */
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 2164021f3b5f6548b96ac067aac67bd7874dcd10..9a7b36f0a4255de5996fd60e093c3e9d95566471 100644 (file)
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -319,6 +319,7 @@ enum {
        STRIPE_BIOFILL_RUN,
        STRIPE_COMPUTE_RUN,
        STRIPE_OPS_REQ_PENDING,
+       STRIPE_ON_UNPLUG_LIST,
 };
 
 /*