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SubjectRe: [PATCH v2 3/7] blkcg: associate a request with its blkcg_gq instead of request_list
On Mon, Nov 13, 2017 at 12:15:23PM -0800, Tejun Heo wrote:
> From c856a199ec70e4022e997609f1b17b9106408777 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@kernel.org>
> Date: Mon, 13 Nov 2017 12:11:57 -0800
>
> On the legacy request_queue, each blkcg_gq has a dedicated
> request_list that requests for the cgroup are allocated from. Each
> request points to the originating request_list and cgroup membership
> can be determined by examining which cgroup the associated
> request_list belongs to.
>
> This doesn't work for blk-mq which doesn't use request_list. Let's
> associate each request with the blkcg_gq directly. Except for minor
> wrapper changes, this doesn't affect the legacy request_queue and will
> allow blk-mq to track each request's cgroup association.
>
> v2: Build fix for !CONFIG_BLK_CGROUP.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
> block/blk-mq.c | 2 +-
> include/linux/blk-cgroup.h | 7 +++++--
> include/linux/blkdev.h | 2 +-
> 3 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 98a1860..af958c4 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -306,7 +306,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
> rq->part = NULL;
> rq->start_time = jiffies;
> #ifdef CONFIG_BLK_CGROUP
> - rq->rl = NULL;
> + rq->blkg = NULL;
> set_start_time_ns(rq);
> rq->io_start_time_ns = 0;
> #endif
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index c0d4736..47db75a 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -463,7 +463,7 @@ static inline void blk_put_rl(struct request_list *rl)
> */
> static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
> {
> - rq->rl = rl;
> + rq->blkg = rl->blkg;
> }

After patch 5, we don't really need the blk_put_rl, blk_get_rl, blk_rq_set_rl
functions. I'd like to delete them and only keep blk_rq_rl. The name
blk_rq_set_rl is confusing too.

Thanks,
Shaohua
> /**
> @@ -474,7 +474,10 @@ static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
> */
> static inline struct request_list *blk_rq_rl(struct request *rq)
> {
> - return rq->rl;
> + if (!rq->blkg->parent)
> + return &rq->q->root_rl;
> + else
> + return &rq->blkg->rl;
> }
>
> struct request_list *__blk_queue_next_rl(struct request_list *rl,
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 8da6637..6ec1067 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -206,7 +206,7 @@ struct request {
> unsigned long start_time;
> struct blk_issue_stat issue_stat;
> #ifdef CONFIG_BLK_CGROUP
> - struct request_list *rl; /* rl this rq is alloced from */
> + struct blkcg_gq *blkg; /* blkg of this rq */
> unsigned long long start_time_ns;
> unsigned long long io_start_time_ns; /* when passed to hardware */
> #endif
> --
> 2.9.5
>

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