blk-mq: only allocate a single mq_map per tag_set

The mapping is identical for all queues in a tag_set, so stop wasting
memory for building multiple.  Note that for now I've kept the mq_map
pointer in the request_queue, but we'll need to investigate if we can
remove it without suffering too much from the additional pointer chasing.
The same would apply to the mq_ops pointer as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 15 insertions, 8 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ffc9d4a3dbbd..c9499f118ef6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1973,7 +1973,6 @@ void blk_mq_release(struct request_queue *q)
                 kfree(hctx);
         }
 
-        kfree(q->mq_map);
         q->mq_map = NULL;
 
         kfree(q->queue_hw_ctx);
@@ -2072,9 +2071,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
         if (!q->queue_hw_ctx)
                 goto err_percpu;
 
-        q->mq_map = blk_mq_make_queue_map(set);
-        if (!q->mq_map)
-                goto err_map;
+        q->mq_map = set->mq_map;
 
         blk_mq_realloc_hw_ctxs(set, q);
         if (!q->nr_hw_queues)
@@ -2124,8 +2121,6 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
         return q;
 
 err_hctxs:
-        kfree(q->mq_map);
-err_map:
         kfree(q->queue_hw_ctx);
 err_percpu:
         free_percpu(q->queue_ctx);
@@ -2347,14 +2342,22 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
         if (!set->tags)
                 return -ENOMEM;
 
+        set->mq_map = blk_mq_make_queue_map(set);
+        if (!set->mq_map)
+                goto out_free_tags;
+
         if (blk_mq_alloc_rq_maps(set))
-                goto enomem;
+                goto out_free_mq_map;
 
         mutex_init(&set->tag_list_lock);
         INIT_LIST_HEAD(&set->tag_list);
 
         return 0;
-enomem:
+
+out_free_mq_map:
+        kfree(set->mq_map);
+        set->mq_map = NULL;
+out_free_tags:
         kfree(set->tags);
         set->tags = NULL;
         return -ENOMEM;
@@ -2370,6 +2373,9 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
                         blk_mq_free_rq_map(set, set->tags[i], i);
         }
 
+        kfree(set->mq_map);
+        set->mq_map = NULL;
+
         kfree(set->tags);
         set->tags = NULL;
 }
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 60ef14cbcd2d..deda16a9bde4 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -67,6 +67,7 @@ struct blk_mq_hw_ctx {
 };
 
 struct blk_mq_tag_set {
+        unsigned int            *mq_map;
         struct blk_mq_ops       *ops;
         unsigned int            nr_hw_queues;
         unsigned int            queue_depth;    /* max hw supported */