linux-kernel - Re: [PATCH v6 1/5] writeback, cgroup: switch to rcu_work API in inode_switch

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Date:   Thu, 3 Jun 2021 10:46:39 +0200
From:   Jan Kara <jack@...e.cz>
To:     Roman Gushchin <guro@...com>
Cc:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Dennis Zhou <dennis@...nel.org>,
        Dave Chinner <dchinner@...hat.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH v6 1/5] writeback, cgroup: switch to rcu_work API in
 inode_switch_wbs()

On Wed 02-06-21 17:55:13, Roman Gushchin wrote:
> Inode's wb switching requires two steps divided by an RCU grace
> period. It's currently implemented as an RCU callback
> inode_switch_wbs_rcu_fn(), which schedules inode_switch_wbs_work_fn()
> as a work.
> 
> Switching to the rcu_work API allows to do the same in a cleaner and
> slightly shorter form.
> 
> Signed-off-by: Roman Gushchin <guro@...com>

Looks good to me. You can add:

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

								Honza

> ---
>  fs/fs-writeback.c | 18 ++++--------------
>  1 file changed, 4 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index e91980f49388..1f51857e41d1 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -335,8 +335,7 @@ struct inode_switch_wbs_context {
>  	struct inode		*inode;
>  	struct bdi_writeback	*new_wb;
>  
> -	struct rcu_head		rcu_head;
> -	struct work_struct	work;
> +	struct rcu_work		work;
>  };
>  
>  static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
> @@ -352,7 +351,7 @@ static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
>  static void inode_switch_wbs_work_fn(struct work_struct *work)
>  {
>  	struct inode_switch_wbs_context *isw =
> -		container_of(work, struct inode_switch_wbs_context, work);
> +		container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
>  	struct inode *inode = isw->inode;
>  	struct backing_dev_info *bdi = inode_to_bdi(inode);
>  	struct address_space *mapping = inode->i_mapping;
> @@ -469,16 +468,6 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
>  	atomic_dec(&isw_nr_in_flight);
>  }
>  
> -static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
> -{
> -	struct inode_switch_wbs_context *isw = container_of(rcu_head,
> -				struct inode_switch_wbs_context, rcu_head);
> -
> -	/* needs to grab bh-unsafe locks, bounce to work item */
> -	INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
> -	queue_work(isw_wq, &isw->work);
> -}
> -
>  /**
>   * inode_switch_wbs - change the wb association of an inode
>   * @inode: target inode
> @@ -534,7 +523,8 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
>  	 * lock so that stat transfer can synchronize against them.
>  	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
>  	 */
> -	call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
> +	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
> +	queue_rcu_work(isw_wq, &isw->work);
>  
>  	atomic_inc(&isw_nr_in_flight);
>  	return;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR