[PATCH 2/2] blk-mq: immediately dispatch big size request

[Shaohua Li]

This is corresponding part for blk-mq. Disk with multiple hardware
queues doesn't need this as we only hold 1 request at most.

Signed-off-by: Shaohua Li <s...@fb.com>
---
 block/blk-mq.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f3d27a6..9612306 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1401,13 +1401,18 @@ static blk_qc_t blk_sq_make_request(struct 
request_queue *q, struct bio *bio)
         */
        plug = current->plug;
        if (plug) {
+               struct request *first = NULL;
+
                blk_mq_bio_to_request(rq, bio);
                if (!request_count)
                        trace_block_plug(q);
+               else
+                       first = list_entry_rq(plug->mq_list.next);
 
                blk_mq_put_ctx(data.ctx);
 
-               if (request_count >= BLK_MAX_REQUEST_COUNT) {
+               if (request_count >= BLK_MAX_REQUEST_COUNT || (first &&
+                   blk_rq_bytes(first) >= BLK_PLUG_FLUSH_SIZE)) {
                        blk_flush_plug_list(plug, false);
                        trace_block_plug(q);
                }
-- 
2.9.3