[RFC,1/2] block: record blkcss in request

Commit Message

Shaohua Li Oct. 4, 2017, 5:41 p.m. UTC

From: Shaohua Li <[e-mail]>

Currently we record block css info in bio but not in request. Normally
we can get a request's css from its bio, but in some situations, we
can't access request's bio, for example, after blk_update_request. Add
the css to request, so we can access css through the life cycle of a
request.

Signed-off-by: Shaohua Li <[e-mail]>
---
 block/blk-core.c       | 12 ++++++++++++
 include/linux/blkdev.h |  1 +
 2 files changed, 13 insertions(+)

Comments

Tejun Heo Oct. 4, 2017, 5:51 p.m. UTC | #1

Hello, Shaohua.

On Wed, Oct 04, 2017 at 10:41:19AM -0700, Shaohua Li wrote:
> From: Shaohua Li <[e-mail]>
> 
> Currently we record block css info in bio but not in request. Normally
> we can get a request's css from its bio, but in some situations, we
> can't access request's bio, for example, after blk_update_request. Add
> the css to request, so we can access css through the life cycle of a
> request.

Each request comes from cgroup specific request_list, so given a
request, its blkcg membership can is accessible through

	request->rl->blkg->blkcg

Thanks.

Shaohua Li Oct. 4, 2017, 6:02 p.m. UTC | #2

On Wed, Oct 04, 2017 at 10:51:49AM -0700, Tejun Heo wrote:
> Hello, Shaohua.
> 
> On Wed, Oct 04, 2017 at 10:41:19AM -0700, Shaohua Li wrote:
> > From: Shaohua Li <[e-mail]>
> > 
> > Currently we record block css info in bio but not in request. Normally
> > we can get a request's css from its bio, but in some situations, we
> > can't access request's bio, for example, after blk_update_request. Add
> > the css to request, so we can access css through the life cycle of a
> > request.
> 
> Each request comes from cgroup specific request_list, so given a
> request, its blkcg membership can is accessible through
> 
> 	request->rl->blkg->blkcg

Nice. Seems only used for legacy queue though.

Thanks,
Shaohua

Tejun Heo Oct. 4, 2017, 6:05 p.m. UTC | #3

On Wed, Oct 04, 2017 at 11:02:46AM -0700, Shaohua Li wrote:
> > Each request comes from cgroup specific request_list, so given a
> > request, its blkcg membership can is accessible through
> > 
> > 	request->rl->blkg->blkcg
> 
> Nice. Seems only used for legacy queue though.

Ah, you're right.  rl isn't used for mq at all, so yeah, we probably
should propagate the association through rq.

Thanks.

Patch

diff --git a/block/blk-core.c b/block/blk-core.c
index adb064a..07f8f7e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1551,6 +1551,11 @@  void __blk_put_request(struct request_queue *q, struct request *req)
 		return;
 	}
 
+#ifdef CONFIG_BLK_CGROUP
+	if (req->css)
+		css_put(req->css);
+#endif
+
 	lockdep_assert_held(q->queue_lock);
 
 	blk_pm_put_request(req);
@@ -3094,6 +3099,13 @@  void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
 		rq->rq_flags |= RQF_QUIET;
 	if (bio->bi_disk)
 		rq->rq_disk = bio->bi_disk;
+#ifdef CONFIG_BLK_CGROUP
+	rq->css = NULL;
+	if (bio->bi_css) {
+		rq->css = bio->bi_css;
+		css_get(rq->css);
+	}
+#endif
 }
 
 #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 02fa42d..cdd3aeb 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -208,6 +208,7 @@  struct request {
 	struct request_list *rl;		/* rl this rq is alloced from */
 	unsigned long long start_time_ns;
 	unsigned long long io_start_time_ns;    /* when passed to hardware */
+	struct cgroup_subsys_state *css;
 #endif
 	/* Number of scatter-gather DMA addr+len pairs after
 	 * physical address coalescing is performed.