[PATCH V5 6/8] block: introduce .last_merge and .hash to blk_mq_ctx

[Ming Lei]

Prepare for supporting bio merge to sw queue if no
blk-mq io scheduler is taken.

Tested-by: Oleksandr Natalenko <oleksa...@natalenko.name>
Tested-by: Tom Nguyen <tom81...@gmail.com>
Tested-by: Paolo Valente <paolo.vale...@linaro.org>
Signed-off-by: Ming Lei <ming....@redhat.com>
---
 block/blk-mq.h   |  4 ++++
 block/blk.h      |  3 +++
 block/elevator.c | 22 +++++++++++++++++++---
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.h b/block/blk-mq.h
index 5bca6ce1f01d..85ea8615fecf 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -18,6 +18,10 @@ struct blk_mq_ctx {
        unsigned long           rq_dispatched[2];
        unsigned long           rq_merged;
 
+       /* bio merge via request hash table */
+       struct request          *last_merge;
+       DECLARE_HASHTABLE(hash, ELV_HASH_BITS);
+
        /* incremented at completion time */
        unsigned long           ____cacheline_aligned_in_smp rq_completed[2];
 
diff --git a/block/blk.h b/block/blk.h
index eb3436d4a73f..fa4f232afc18 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -198,6 +198,9 @@ static inline struct request *rqhash_find(struct hlist_head 
*hash, sector_t offs
        return NULL;
 }
 
+enum elv_merge elv_merge_ctx(struct request_queue *q, struct request **req,
+                struct bio *bio, struct blk_mq_ctx *ctx);
+
 void blk_insert_flush(struct request *rq);
 
 static inline struct request *__elv_next_request(struct request_queue *q)
diff --git a/block/elevator.c b/block/elevator.c
index 2424aea85393..0e13e5c18982 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -471,6 +471,13 @@ enum elv_merge elv_merge(struct request_queue *q, struct 
request **req,
        return __elv_merge(q, req, bio, q->elevator->hash, q->last_merge);
 }
 
+enum elv_merge elv_merge_ctx(struct request_queue *q, struct request **req,
+               struct bio *bio, struct blk_mq_ctx *ctx)
+{
+       WARN_ON_ONCE(!q->mq_ops);
+       return __elv_merge(q, req, bio, ctx->hash, ctx->last_merge);
+}
+
 /*
  * Attempt to do an insertion back merge. Only check for the case where
  * we can append 'rq' to an existing request, so we can throw 'rq' away
@@ -516,16 +523,25 @@ void elv_merged_request(struct request_queue *q, struct 
request *rq,
                enum elv_merge type)
 {
        struct elevator_queue *e = q->elevator;
+       struct hlist_head *hash = e->hash;
+
+       /* we do bio merge on blk-mq sw queue */
+       if (q->mq_ops && !e) {
+               rq->mq_ctx->last_merge = rq;
+               hash = rq->mq_ctx->hash;
+               goto reposition;
+       }
+
+       q->last_merge = rq;
 
        if (e->uses_mq && e->type->ops.mq.request_merged)
                e->type->ops.mq.request_merged(q, rq, type);
        else if (!e->uses_mq && e->type->ops.sq.elevator_merged_fn)
                e->type->ops.sq.elevator_merged_fn(q, rq, type);
 
+ reposition:
        if (type == ELEVATOR_BACK_MERGE)
-               elv_rqhash_reposition(q, rq);
-
-       q->last_merge = rq;
+               rqhash_reposition(hash, rq);
 }
 
 void elv_merge_requests(struct request_queue *q, struct request *rq,
-- 
2.9.5