[patch]blk: use correct sectors limitation for discard request

[Shaohua Li]

Subject: blk: use correct sectors limitation for discard request

max_discard_sectors doesn't equal to max_sectors/max_hw_sectors. Without 
this,
discard request merge might be ignored.

Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
---
 block/blk-merge.c      |   13 ++++++++-----
 include/linux/blkdev.h |    5 +++++
 2 files changed, 13 insertions(+), 5 deletions(-)

Index: linux/block/blk-merge.c
===================================================================
--- linux.orig/block/blk-merge.c	2012-03-14 09:53:15.574255985 +0800
+++ linux/block/blk-merge.c	2012-03-14 11:06:01.504462095 +0800
@@ -228,9 +228,11 @@ no_merge:
 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 		     struct bio *bio)
 {
-	unsigned short max_sectors;
+	unsigned int max_sectors;

-	if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
+	if (unlikely(req->cmd_flags & REQ_DISCARD))
+		max_sectors = queue_max_discard_sectors(q);
+	else if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
 		max_sectors = queue_max_hw_sectors(q);
 	else
 		max_sectors = queue_max_sectors(q);
@@ -252,14 +254,15 @@ int ll_back_merge_fn(struct request_queu
 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 		      struct bio *bio)
 {
-	unsigned short max_sectors;
+	unsigned int max_sectors;

-	if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
+	if (unlikely(req->cmd_flags & REQ_DISCARD))
+		max_sectors = queue_max_discard_sectors(q);
+	else if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
 		max_sectors = queue_max_hw_sectors(q);
 	else
 		max_sectors = queue_max_sectors(q);

-
 	if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
 		req->cmd_flags |= REQ_NOMERGE;
 		if (req == q->last_merge)
Index: linux/include/linux/blkdev.h
===================================================================
--- linux.orig/include/linux/blkdev.h	2012-03-14 10:17:19.523960440 +0800
+++ linux/include/linux/blkdev.h	2012-03-14 10:57:22.324465357 +0800
@@ -1006,6 +1006,11 @@ static inline unsigned int queue_max_hw_
 	return q->limits.max_hw_sectors;
 }

+static inline unsigned int queue_max_discard_sectors(struct 
request_queue *q)
+{
+	return q->limits.max_discard_sectors;
+}
+
 static inline unsigned short queue_max_segments(struct request_queue *q)
 {
 	return q->limits.max_segments;
--
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