linux-kernel - Re: [PATCH 1/6] blk-cgroup: factor out a helper to read rwstat counter

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Date:   Thu, 6 Jun 2019 15:03:04 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>
CC:     Paolo Valente <paolo.valente@...aro.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] blk-cgroup: factor out a helper to read rwstat
 counter

Looks good to me.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@....com>

On 06/06/2019 03:27 AM, Christoph Hellwig wrote:
> Trying to break up the crazy statements to something readable.
> Also switch to an unsigned counter as it can't ever turn negative.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   block/blk-cgroup.c         | 5 ++---
>   include/linux/blk-cgroup.h | 7 +++++++
>   2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index b97b479e4f64..6f79ace02be4 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -750,7 +750,7 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
>   	struct blkcg_gq *pos_blkg;
>   	struct cgroup_subsys_state *pos_css;
>   	struct blkg_rwstat sum = { };
> -	int i;
> +	unsigned int i;
>
>   	lockdep_assert_held(&blkg->q->queue_lock);
>
> @@ -767,8 +767,7 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
>   			rwstat = (void *)pos_blkg + off;
>
>   		for (i = 0; i < BLKG_RWSTAT_NR; i++)
> -			atomic64_add(atomic64_read(&rwstat->aux_cnt[i]) +
> -				percpu_counter_sum_positive(&rwstat->cpu_cnt[i]),
> +			atomic64_add(blkg_rwstat_read_counter(rwstat, i),
>   				&sum.aux_cnt[i]);
>   	}
>   	rcu_read_unlock();
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index 76c61318fda5..06236f56a840 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -198,6 +198,13 @@ int blkcg_activate_policy(struct request_queue *q,
>   void blkcg_deactivate_policy(struct request_queue *q,
>   			     const struct blkcg_policy *pol);
>
> +static inline u64 blkg_rwstat_read_counter(struct blkg_rwstat *rwstat,
> +		unsigned int idx)
> +{
> +	return atomic64_read(&rwstat->aux_cnt[idx]) +
> +		percpu_counter_sum_positive(&rwstat->cpu_cnt[idx]);
> +}
> +
>   const char *blkg_dev_name(struct blkcg_gq *blkg);
>   void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
>   		       u64 (*prfill)(struct seq_file *,
>