Merge branch 'for-linus' of git://git.kernel.dk/linux-2.6-block

[linux-flexiantxendom0-natty.git] / block / blk-throttle.c

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 381b09b..a89043a 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -168,7 +168,15 @@ static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
         * tree of blkg (instead of traversing through hash list all
         * the time.
         */
-       tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
+
+       /*
+        * This is the common case when there are no blkio cgroups.
+        * Avoid lookup in this case
+        */
+       if (blkcg == &blkio_root_cgroup)
+               tg = &td->root_tg;
+       else
+               tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
 
        /* Fill in device details for root group */
        if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {