linux-kernel - [PATCH] Move the second call to get

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Message-Id: <1211444984.3177.256.camel@ymzhang>
Date:	Thu, 22 May 2008 16:29:44 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>
Subject: [PATCH] Move the second call to get_request to the end of the loop

In function get_request_wait, the second call to get_request could be moved to the end of the while loop,
because if the first call to get_request fails, the second call will fail without sleep.

Signed-off-by: Zhang Yanmin <yanmin.zhang@...el.com>

---

--- linux-2.6.26-rc3/block/blk-core.c	2008-05-19 07:17:18.000000000 +0800
+++ linux-2.6.26-rc3_block/block/blk-core.c	2008-05-22 07:00:15.000000000 +0800
@@ -806,35 +806,32 @@ static struct request *get_request_wait(
 	rq = get_request(q, rw_flags, bio, GFP_NOIO);
 	while (!rq) {
 		DEFINE_WAIT(wait);
+		struct io_context *ioc;
 		struct request_list *rl = &q->rq;
 
 		prepare_to_wait_exclusive(&rl->wait[rw], &wait,
 				TASK_UNINTERRUPTIBLE);
 
-		rq = get_request(q, rw_flags, bio, GFP_NOIO);
-
-		if (!rq) {
-			struct io_context *ioc;
+		blk_add_trace_generic(q, bio, rw, BLK_TA_SLEEPRQ);
 
-			blk_add_trace_generic(q, bio, rw, BLK_TA_SLEEPRQ);
-
-			__generic_unplug_device(q);
-			spin_unlock_irq(q->queue_lock);
-			io_schedule();
+		__generic_unplug_device(q);
+		spin_unlock_irq(q->queue_lock);
+		io_schedule();
 
-			/*
-			 * After sleeping, we become a "batching" process and
-			 * will be able to allocate at least one request, and
-			 * up to a big batch of them for a small period time.
-			 * See ioc_batching, ioc_set_batching
-			 */
-			ioc = current_io_context(GFP_NOIO, q->node);
-			ioc_set_batching(q, ioc);
+		/*
+		 * After sleeping, we become a "batching" process and
+		 * will be able to allocate at least one request, and
+		 * up to a big batch of them for a small period time.
+		 * See ioc_batching, ioc_set_batching
+		 */
+		ioc = current_io_context(GFP_NOIO, q->node);
+		ioc_set_batching(q, ioc);
 
-			spin_lock_irq(q->queue_lock);
-		}
+		spin_lock_irq(q->queue_lock);
 		finish_wait(&rl->wait[rw], &wait);
-	}
+
+		rq = get_request(q, rw_flags, bio, GFP_NOIO);
+	};
 
 	return rq;
 }


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