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SubjectRe: [PATCH 4/7] blkcg: refactor blkcg_gq lookup and creation in blkcg_bio_issue_check()
On Sun, Nov 12, 2017 at 02:26:10PM -0800, Tejun Heo wrote:
> blkcg_bio_issue_check() open codes blkcg_gq lookup and creation using
> blkg_lookup() and blkg_lookup_create(). Refactor the code so that
>
> * blkg_lookup_create() is renamed to blkcg_lookup_create_locked().
>
> * blkg_lookup_create() is now a new function which encapsulates the
> RCU protected lookup and queue_locked protected creation.
>
> * blkg_lookup_create() is guaranteed to return a non-NULL blkcg_gq.
> The NULL checks are removed from the users.
>
> This is pure refactoring and doesn't introduce any functional changes.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>

Reviewed-by: Shaohua Li <shli@kernel.org>
> ---
> block/blk-cgroup.c | 6 +++---
> block/blk-throttle.c | 2 +-
> include/linux/blk-cgroup.h | 32 +++++++++++++++++++++-----------
> 3 files changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 60a4486..490b0a6 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -290,7 +290,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
> }
>
> /**
> - * blkg_lookup_create - lookup blkg, try to create one if not there
> + * blkg_lookup_create_locked - lookup blkg, try to create one if not there
> * @blkcg: blkcg of interest
> * @q: request_queue of interest
> *
> @@ -303,8 +303,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
> * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
> * dead and bypassing, returns ERR_PTR(-EBUSY).
> */
> -struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> - struct request_queue *q)
> +struct blkcg_gq *blkg_lookup_create_locked(struct blkcg *blkcg,
> + struct request_queue *q)
> {
> struct blkcg_gq *blkg;
>
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 8631763..1e6916b 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -2123,7 +2123,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
> struct bio *bio)
> {
> struct throtl_qnode *qn = NULL;
> - struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
> + struct throtl_grp *tg = blkg_to_tg(blkg);
> struct throtl_service_queue *sq;
> bool rw = bio_data_dir(bio);
> bool throttled = false;
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index b5721d32..1de5158 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -172,8 +172,8 @@ extern struct cgroup_subsys_state * const blkcg_root_css;
>
> struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
> struct request_queue *q, bool update_hint);
> -struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> - struct request_queue *q);
> +struct blkcg_gq *blkg_lookup_create_locked(struct blkcg *blkcg,
> + struct request_queue *q);
> int blkcg_init_queue(struct request_queue *q);
> void blkcg_drain_queue(struct request_queue *q);
> void blkcg_exit_queue(struct request_queue *q);
> @@ -680,6 +680,24 @@ static inline bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg
> struct bio *bio) { return false; }
> #endif
>
> +static inline struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> + struct request_queue *q)
> +{
> + struct blkcg_gq *blkg;
> +
> + blkg = blkg_lookup(blkcg, q);
> + if (likely(blkg))
> + return blkg;
> +
> + spin_lock_irq(q->queue_lock);
> + blkg = blkg_lookup_create_locked(blkcg, q);
> + spin_unlock_irq(q->queue_lock);
> + if (likely(!IS_ERR(blkg)))
> + return blkg;
> + else
> + return q->root_blkg;
> +}
> +
> static inline bool blkcg_bio_issue_check(struct request_queue *q,
> struct bio *bio)
> {
> @@ -693,19 +711,11 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
> /* associate blkcg if bio hasn't attached one */
> bio_associate_blkcg(bio, &blkcg->css);
>
> - blkg = blkg_lookup(blkcg, q);
> - if (unlikely(!blkg)) {
> - spin_lock_irq(q->queue_lock);
> - blkg = blkg_lookup_create(blkcg, q);
> - if (IS_ERR(blkg))
> - blkg = NULL;
> - spin_unlock_irq(q->queue_lock);
> - }
> + blkg = blkg_lookup_create(blkcg, q);
>
> throtl = blk_throtl_bio(q, blkg, bio);
>
> if (!throtl) {
> - blkg = blkg ?: q->root_blkg;
> blkg_rwstat_add(&blkg->stat_bytes, bio->bi_opf,
> bio->bi_iter.bi_size);
> blkg_rwstat_add(&blkg->stat_ios, bio->bi_opf, 1);
> --
> 2.9.5
>

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