blk-mq: immediately dispatch big size request

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 <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8d3de5bd4d6f..077c2416a955 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1453,13 +1453,18 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
          */
         plug = current->plug;
         if (plug) {
+                struct request *last = NULL;
+
                 blk_mq_bio_to_request(rq, bio);
                 if (!request_count)
                         trace_block_plug(q);
+                else
+                        last = list_entry_rq(plug->mq_list.prev);
 
                 blk_mq_put_ctx(data.ctx);
 
-                if (request_count >= BLK_MAX_REQUEST_COUNT) {
+                if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&
+                    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
                         blk_flush_plug_list(plug, false);
                         trace_block_plug(q);
                 }