[PATCH 07/13] blk-mq: only allocate a single mq_map per tag_set

[Christoph Hellwig]

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 <h...@lst.de>
---
 block/blk-mq.c         | 22 ++++++++++++++--------
 include/linux/blk-mq.h |  1 +
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b29e7b2..15c36c1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1963,7 +1963,6 @@ void blk_mq_release(struct request_queue *q)
                kfree(hctx);
        }
 
-       kfree(q->mq_map);
        q->mq_map = NULL;
 
        kfree(q->queue_hw_ctx);
@@ -2062,9 +2061,7 @@ 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)
@@ -2114,8 +2111,6 @@ 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);
@@ -2337,14 +2332,22 @@ 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;
@@ -2360,6 +2363,9 @@ 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 e43bbff..a572227 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -65,6 +65,7 @@ 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 */
-- 
2.1.4