On Thu, 2017-05-25 at 17:09 +0800, Ming Lei wrote: > Another big issue is that 'srcu_struct' is very big, which shouldn't > be embedded into hctx, since we only have one real user of > BLK_MQ_F_BLOCKING. > > So I will fix that too.
Hello Ming, Is something like the (untested) patch below perhaps what you had in mind? Subject: [PATCH] blk-mq: Reduce blk_mq_hw_ctx size Since the srcu structure is rather large (184 bytes on an x86-64 system), only allocate it if needed. Reported-by: Ming Lei <[email protected]> --- block/blk-mq.c | 13 ++++++++++++- include/linux/blk-mq.h | 5 +++-- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 1e330de4e3c5..15b7d4077638 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2233,6 +2233,17 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set) } EXPORT_SYMBOL(blk_mq_init_queue); +static int blk_mq_hw_ctx_size(struct request_queue *q) +{ + BUILD_BUG_ON(ALIGN(offsetof(struct blk_mq_hw_ctx, queue_rq_srcu) + + sizeof(((struct blk_mq_hw_ctx *)NULL)->queue_rq_srcu), 64) != + sizeof(struct blk_mq_hw_ctx)); + + return q->tag_set->flags & BLK_MQ_F_BLOCKING ? + sizeof(struct blk_mq_hw_ctx) : + offsetof(struct blk_mq_hw_ctx, queue_rq_srcu); +} + static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, struct request_queue *q) { @@ -2247,7 +2258,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, continue; node = blk_mq_hw_queue_to_node(q->mq_map, i); - hctxs[i] = kzalloc_node(sizeof(struct blk_mq_hw_ctx), + hctxs[i] = kzalloc_node(blk_mq_hw_ctx_size(q), GFP_KERNEL, node); if (!hctxs[i]) break; diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index c0d59330b5e0..8467e1f83524 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -39,8 +39,6 @@ struct blk_mq_hw_ctx { struct blk_mq_tags *tags; struct blk_mq_tags *sched_tags; - struct srcu_struct queue_rq_srcu; - unsigned long queued; unsigned long run; #define BLK_MQ_MAX_DISPATCH_ORDER 7 @@ -62,6 +60,9 @@ struct blk_mq_hw_ctx { struct dentry *debugfs_dir; struct dentry *sched_debugfs_dir; #endif + + /* Must be the last member - see also blk_mq_hw_ctx_size(). */ + struct srcu_struct queue_rq_srcu; }; struct blk_mq_tag_set { -- 2.12.2
