[PATCH V2 1/2] blk-mq: abstract out blk-mq-sched rq list iteration bio merge helper

[Jianchao Wang]

From: Jens Axboe <ax...@kernel.dk>

No functional changes in this patch, just a prep patch for utilizing
this in an IO scheduler.

Signed-off-by: Jens Axboe <ax...@kernel.dk>
---
 block/blk-mq-sched.c   | 34 ++++++++++++++++++++++++----------
 include/linux/blk-mq.h |  3 ++-
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 25c14c5..b0f2c2a 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -268,19 +268,16 @@ bool blk_mq_sched_try_merge(struct request_queue *q, 
struct bio *bio,
 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 
 /*
- * Reverse check our software queue for entries that we could potentially
- * merge with. Currently includes a hand-wavy stop count of 8, to not spend
- * too much time checking for merges.
+ * Iterate list of requests and see if we can merge this bio with any
+ * of them.
  */
-static bool blk_mq_attempt_merge(struct request_queue *q,
-                                struct blk_mq_ctx *ctx, struct bio *bio)
+bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
+                          struct bio *bio)
 {
        struct request *rq;
        int checked = 8;
 
-       lockdep_assert_held(&ctx->lock);
-
-       list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
+       list_for_each_entry_reverse(rq, list, queuelist) {
                bool merged = false;
 
                if (!checked--)
@@ -305,13 +302,30 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
                        continue;
                }
 
-               if (merged)
-                       ctx->rq_merged++;
                return merged;
        }
 
        return false;
 }
+EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
+
+/*
+ * Reverse check our software queue for entries that we could potentially
+ * merge with. Currently includes a hand-wavy stop count of 8, to not spend
+ * too much time checking for merges.
+ */
+static bool blk_mq_attempt_merge(struct request_queue *q,
+                                struct blk_mq_ctx *ctx, struct bio *bio)
+{
+       lockdep_assert_held(&ctx->lock);
+
+       if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
+               ctx->rq_merged++;
+               return true;
+       }
+
+       return false;
+}
 
 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 {
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index ebc34a5..fb35517 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -259,7 +259,8 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool 
at_head,
 void blk_mq_kick_requeue_list(struct request_queue *q);
 void blk_mq_delay_kick_requeue_list(struct request_queue *q, unsigned long 
msecs);
 void blk_mq_complete_request(struct request *rq);
-
+bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
+                          struct bio *bio);
 bool blk_mq_queue_stopped(struct request_queue *q);
 void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx);
 void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx);
-- 
2.7.4