X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=block%2Fblk-tag.c;h=2e5cfeb59333ecc088576324f1d6e0e88faf3bed;hb=1d2235152dc745c6d94bedb550fea84cffdbf768;hp=8a99688eb1b1951e35586fb2861cf6e86917c756;hpb=710027a48ede75428cc68eaa8ae2269b1e356e2c;p=safe%2Fjmp%2Flinux-2.6

diff --git a/block/blk-tag.c b/block/blk-tag.c
index 8a99688..2e5cfeb 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -158,7 +158,6 @@ fail:
 /**
  * blk_init_tags - initialize the tag info for an external tag map
  * @depth:	the maximum queue depth supported
- * @tags: the tag to use
  **/
 struct blk_queue_tag *blk_init_tags(int depth)
 {
@@ -337,6 +336,7 @@ EXPORT_SYMBOL(blk_queue_end_tag);
 int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 {
 	struct blk_queue_tag *bqt = q->queue_tags;
+	unsigned max_depth;
 	int tag;
 
 	if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
@@ -350,10 +350,22 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 	/*
 	 * Protect against shared tag maps, as we may not have exclusive
 	 * access to the tag map.
+	 *
+	 * We reserve a few tags just for sync IO, since we don't want
+	 * to starve sync IO on behalf of flooding async IO.
 	 */
+	max_depth = bqt->max_depth;
+	if (!rq_is_sync(rq) && max_depth > 1) {
+		max_depth -= 2;
+		if (!max_depth)
+			max_depth = 1;
+		if (q->in_flight[0] > max_depth)
+			return 1;
+	}
+
 	do {
-		tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
-		if (tag >= bqt->max_depth)
+		tag = find_first_zero_bit(bqt->tag_map, max_depth);
+		if (tag >= max_depth)
 			return 1;
 
 	} while (test_and_set_bit_lock(tag, bqt->tag_map));
@@ -365,7 +377,7 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 	rq->cmd_flags |= REQ_QUEUED;
 	rq->tag = tag;
 	bqt->tag_index[tag] = rq;
-	blkdev_dequeue_request(rq);
+	blk_start_request(rq);
 	list_add(&rq->queuelist, &q->tag_busy_list);
 	return 0;
 }