linux-kernel - Re: [PATCH] writeback: fix delayed sync(2)

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Message-ID: <20130920230256.GB8763@mtj.dyndns.org>
Date:	Fri, 20 Sep 2013 18:02:56 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Maxim Patlasov <MPatlasov@...allels.com>
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	fengguang.wu@...el.com, jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] writeback: fix delayed sync(2)

Hello,

On Fri, Sep 20, 2013 at 04:52:26PM +0400, Maxim Patlasov wrote:
> @@ -294,7 +294,7 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
>  	unsigned long timeout;
>  
>  	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> -	mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
> +	queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);

Hmmm... this at least requires comment explaining why
mod_delayed_work() doesn't work here.  Also, I wonder whether what we
need is a function which either queues if !pending and shortens timer
if pending.  This is a relatively common pattern and the suggested fix
is subtle and fragile.

Thanks.

-- 
tejun
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