blk-mq: cleanup and rename __blk_mq_alloc_request

The newly added loop for the cached requests in __blk_mq_alloc_request
is a little too convoluted for my taste, so unwind it a bit.  Also
rename the function to __blk_mq_alloc_requests now that it can allocate
more than a single request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211012104045.658051-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d9f14d3..98a5d08 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -354,7 +354,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
        return rq;
 }
 
-static struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data)
+static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 {
        struct request_queue *q = data->q;
        struct elevator_queue *e = q->elevator;
@@ -395,36 +395,36 @@ retry:
         */
        do {
                tag = blk_mq_get_tag(data);
-               if (tag != BLK_MQ_NO_TAG) {
-                       rq = blk_mq_rq_ctx_init(data, tag, alloc_time_ns);
-                       if (!--data->nr_tags)
-                               return rq;
-                       if (e || data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
-                               return rq;
-                       rq->rq_next = *data->cached_rq;
-                       *data->cached_rq = rq;
-                       data->flags |= BLK_MQ_REQ_NOWAIT;
-                       continue;
+               if (tag == BLK_MQ_NO_TAG) {
+                       if (data->flags & BLK_MQ_REQ_NOWAIT)
+                               break;
+                       /*
+                        * Give up the CPU and sleep for a random short time to
+                        * ensure that thread using a realtime scheduling class
+                        * are migrated off the CPU, and thus off the hctx that
+                        * is going away.
+                        */
+                       msleep(3);
+                       goto retry;
                }
-               if (data->flags & BLK_MQ_REQ_NOWAIT)
-                       break;
 
-               /*
-                * Give up the CPU and sleep for a random short time to ensure
-                * that thread using a realtime scheduling class are migrated
-                * off the CPU, and thus off the hctx that is going away.
-                */
-               msleep(3);
-               goto retry;
+               rq = blk_mq_rq_ctx_init(data, tag, alloc_time_ns);
+               if (!--data->nr_tags || e ||
+                   (data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
+                       return rq;
+
+               /* link into the cached list */
+               rq->rq_next = *data->cached_rq;
+               *data->cached_rq = rq;
+               data->flags |= BLK_MQ_REQ_NOWAIT;
        } while (1);
 
-       if (data->cached_rq) {
-               rq = *data->cached_rq;
-               *data->cached_rq = rq->rq_next;
-               return rq;
-       }
+       if (!data->cached_rq)
+               return NULL;
 
-       return NULL;
+       rq = *data->cached_rq;
+       *data->cached_rq = rq->rq_next;
+       return rq;
 }
 
 struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
@@ -443,7 +443,7 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
        if (ret)
                return ERR_PTR(ret);
 
-       rq = __blk_mq_alloc_request(&data);
+       rq = __blk_mq_alloc_requests(&data);
        if (!rq)
                goto out_queue_exit;
        rq->__data_len = 0;
@@ -2258,7 +2258,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
                        plug->nr_ios = 1;
                        data.cached_rq = &plug->cached_rq;
                }
-               rq = __blk_mq_alloc_request(&data);
+               rq = __blk_mq_alloc_requests(&data);
                if (unlikely(!rq)) {
                        rq_qos_cleanup(q, bio);
                        if (bio->bi_opf & REQ_NOWAIT)