linux-kernel - [PATCH] blk-cgroup: Initialize ioc->cgroup

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Message-ID: <20110523145539.GA4019@redhat.com>
Date:	Mon, 23 May 2011 10:55:39 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Jens Axboe <jaxboe@...ionio.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Cc:	Paul Bolle <pebolle@...cali.nl>
Subject: [PATCH] blk-cgroup: Initialize ioc->cgroup_changed at ioc creation
 time

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@...hat.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;
--
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