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 <ming.lei@xxxxxxxxxx>
---
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
