block: change the tag sync vs async restriction logic

[safe/jmp/linux-2.6] / block / blk-tag.c

diff --git a/block/blk-tag.c b/block/blk-tag.c
index c260f7c..2e5cfeb 100644 (file)
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -336,7 +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, offset;
+       unsigned max_depth;
        int tag;
 
        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
@@ -355,13 +355,16 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
         * to starve sync IO on behalf of flooding async IO.
         */
        max_depth = bqt->max_depth;
-       if (rq_is_sync(rq))
-               offset = 0;
-       else
-               offset = max_depth >> 2;
+       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_next_zero_bit(bqt->tag_map, max_depth, offset);
+               tag = find_first_zero_bit(bqt->tag_map, max_depth);
                if (tag >= max_depth)
                        return 1;