linux-kernel - Re: [PATCH -next v3] block, bfq: cleanup 'bfqg->online'

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Message-ID: <20230207100714.fv4pfvkt56gb2iqm@quack3>
Date:   Tue, 7 Feb 2023 11:07:14 +0100
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     jack@...e.cz, paolo.valente@...aro.org, axboe@...nel.dk,
        tj@...nel.org, josef@...icpanda.com, linux-block@...r.kernel.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next v3] block, bfq: cleanup 'bfqg->online'

On Thu 02-02-23 21:49:13, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> After commit dfd6200a0954 ("blk-cgroup: support to track if policy is
> online"), there is no need to do this again in bfq.
> 
> However, 'pd->online' is not protected by 'bfqd->lock', in order to make
> sure bfq won't see that 'pd->online' is still set after bfq_pd_offline(),
> clear it before bfq_pd_offline() is called. This is fine because other
> polices doesn't use 'pd->online' and bfq_pd_offline() will move active
> bfqq to root cgroup anyway.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

The patch looks good to me now. Thanks! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> Changes in v3:
>  - in commit message: protected -> not protected, bfq_pd_offline_() ->
>  bfq_pd_offline().
> Changes in v2:
>  - clear 'pd->online' before calling bfq_pd_offline()
> 
>  block/bfq-cgroup.c  | 4 +---
>  block/bfq-iosched.h | 2 --
>  block/blk-cgroup.c  | 2 +-
>  3 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index b42956ab5550..a35136dae713 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -551,7 +551,6 @@ static void bfq_pd_init(struct blkg_policy_data *pd)
>  	bfqg->bfqd = bfqd;
>  	bfqg->active_entities = 0;
>  	bfqg->num_queues_with_pending_reqs = 0;
> -	bfqg->online = true;
>  	bfqg->rq_pos_tree = RB_ROOT;
>  }
>  
> @@ -614,7 +613,7 @@ struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio)
>  			continue;
>  		}
>  		bfqg = blkg_to_bfqg(blkg);
> -		if (bfqg->online) {
> +		if (bfqg->pd.online) {
>  			bio_associate_blkg_from_css(bio, &blkg->blkcg->css);
>  			return bfqg;
>  		}
> @@ -985,7 +984,6 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
>  
>  put_async_queues:
>  	bfq_put_async_queues(bfqd, bfqg);
> -	bfqg->online = false;
>  
>  	spin_unlock_irqrestore(&bfqd->lock, flags);
>  	/*
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 75cc6a324267..69aaee52285a 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -1009,8 +1009,6 @@ struct bfq_group {
>  
>  	/* reference counter (see comments in bfq_bic_update_cgroup) */
>  	refcount_t ref;
> -	/* Is bfq_group still online? */
> -	bool online;
>  
>  	struct bfq_entity entity;
>  	struct bfq_sched_data sched_data;
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index cb110fc51940..a228dfe65253 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -491,9 +491,9 @@ static void blkg_destroy(struct blkcg_gq *blkg)
>  		struct blkcg_policy *pol = blkcg_policy[i];
>  
>  		if (blkg->pd[i] && blkg->pd[i]->online) {
> +			blkg->pd[i]->online = false;
>  			if (pol->pd_offline_fn)
>  				pol->pd_offline_fn(blkg->pd[i]);
> -			blkg->pd[i]->online = false;
>  		}
>  	}
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR