linux-kernel - Re: [PATCH 36/51] writeback: implement bdi_for_each

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Date:	Wed, 1 Jul 2015 09:27:57 +0200
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, jack@...e.cz,
	hch@...radead.org, hannes@...xchg.org,
	linux-fsdevel@...r.kernel.org, vgoyal@...hat.com,
	lizefan@...wei.com, cgroups@...r.kernel.org, linux-mm@...ck.org,
	mhocko@...e.cz, clm@...com, fengguang.wu@...el.com,
	david@...morbit.com, gthelen@...gle.com, khlebnikov@...dex-team.ru
Subject: Re: [PATCH 36/51] writeback: implement bdi_for_each_wb()

On Fri 22-05-15 17:13:50, Tejun Heo wrote:
> This will be used to implement bdi-wide operations which should be
> distributed across all its cgroup bdi_writebacks.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Jan Kara <jack@...e.cz>

One comment below.

> @@ -445,6 +500,14 @@ static inline void wb_blkcg_offline(struct blkcg *blkcg)
>  {
>  }
>  
> +struct wb_iter {
> +	int		next_id;
> +};
> +
> +#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id)		\
> +	for ((iter)->next_id = (start_blkcg_id);			\
> +	     ({	(wb_cur) = !(iter)->next_id++ ? &(bdi)->wb : NULL; }); )
> +

This looks quite confusing. Won't it be easier to understand as:

struct wb_iter {
} __attribute__ ((unused));

#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id) \
  if (((wb_cur) = (!start_blkcg_id ? &(bdi)->wb : NULL)))

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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