[PATCH] blk-cgroup: Initialize ioc->cgroup_changed at ioc creation time

[Vivek Goyal <vgoyal@redhat.com>]

If we don't explicitly initialize it to zero, CFQ might think that
cgroup of ioc has changed and it generates lots of unnecessary calls
to call_for_each_cic(changed_cgroup). Fix it.

cfq_get_io_context()
  cfq_ioc_set_cgroup()
     call_for_each_cic(ioc, changed_cgroup)

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 block/blk-ioc.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6-block/block/blk-ioc.c
===================================================================
--- linux-2.6-block.orig/block/blk-ioc.c	2011-03-08 09:40:58.057296008 -0500
+++ linux-2.6-block/block/blk-ioc.c	2011-05-23 10:33:51.875994035 -0400
@@ -96,6 +96,9 @@ struct io_context *alloc_io_context(gfp_
 		INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
 		INIT_HLIST_HEAD(&ret->cic_list);
 		ret->ioc_data = NULL;
+#if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
+		ret->cgroup_changed = 0;
+#endif
 	}
 
 	return ret;