[PATCH] CFQ: mark must_alloc flag when a cfqq doesn't allocate any request

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Hi Jens,

CFQ judges whether must_alloc flag is set, but never marks this flag.
This patch set must_alloc flag when there is no request allocated by
a cfqq. This change ensures cfqq will get at least one request even
if the queue is full.
Hope it helps.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 block/cfq-iosched.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fd7080e..531a404 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2279,6 +2279,9 @@ static void cfq_put_request(struct request *rq)
 		BUG_ON(!cfqq->allocated[rw]);
 		cfqq->allocated[rw]--;
 
+		if (!(cfqq->allocated[0] + cfqq->allocated[1]))
+			cfq_mark_cfqq_must_alloc(cfqq);
+
 		put_io_context(RQ_CIC(rq)->ioc);
 
 		rq->elevator_private = NULL;
-- 
1.5.4.rc3