linux-kernel - Re: [PATCH 44/51] writeback: implement bdi_wait_for

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Message-ID: <20150701160918.GH7252@quack.suse.cz>
Date:	Wed, 1 Jul 2015 18:09:18 +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 44/51] writeback: implement bdi_wait_for_completion()

On Fri 22-05-15 17:13:58, Tejun Heo wrote:
> If the completion of a wb_writeback_work can be waited upon by setting
> its ->done to a struct completion and waiting on it; however, for
> cgroup writeback support, it's necessary to issue multiple work items
> to multiple bdi_writebacks and wait for the completion of all.
> 
> This patch implements wb_completion which can wait for multiple work
> items and replaces the struct completion with it.  It can be defined
> using DEFINE_WB_COMPLETION_ONSTACK(), used for multiple work items and
> waited for by wb_wait_for_completion().
> 
> Nobody currently issues multiple work items and this patch doesn't
> introduce any behavior changes.

One more thing...

> @@ -161,17 +178,34 @@ static void wb_queue_work(struct bdi_writeback *wb,
>  	trace_writeback_queue(wb->bdi, work);
>  
>  	spin_lock_bh(&wb->work_lock);
> -	if (!test_bit(WB_registered, &wb->state)) {
> -		if (work->done)
> -			complete(work->done);
> +	if (!test_bit(WB_registered, &wb->state))
>  		goto out_unlock;

This seems like a change in behavior. Previously unregistered wbs just
completed the work->done, now you don't complete them. Is that intentional?

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