linux-kernel - Re: [PATCH 05/17] writeback: quit throttling when signal pending

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Message-Id: <20100914172028.C9B2.A69D9226@jp.fujitsu.com>
Date:	Tue, 14 Sep 2010 17:23:56 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com, Neil Brown <neilb@...e.de>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: [PATCH 05/17] writeback: quit throttling when signal pending

> Subject: writeback: quit throttling when fatal signal pending
> From: Wu Fengguang <fengguang.wu@...el.com>
> Date: Wed Sep 08 17:40:22 CST 2010
> 
> This allows quick response to Ctrl-C etc. for impatient users.
> 
> It mainly helps the rare bdi/global dirty exceeded cases.
> In the normal case of not exceeded, it will quit the loop anyway. 
> 
> CC: Neil Brown <neilb@...e.de>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  mm/page-writeback.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> --- linux-next.orig/mm/page-writeback.c	2010-09-12 13:25:23.000000000 +0800
> +++ linux-next/mm/page-writeback.c	2010-09-13 11:39:33.000000000 +0800
> @@ -552,6 +552,9 @@ static void balance_dirty_pages(struct a
>  		__set_current_state(TASK_INTERRUPTIBLE);
>  		io_schedule_timeout(pause);
>  
> +		if (fatal_signal_pending(current))
> +			break;
> +
>  check_exceeded:
>  		/*
>  		 * The bdi thresh is somehow "soft" limit derived from the

I think we need to change callers (e.g. generic_perform_write) too.
Otherwise, plenty write + SIGKILL combination easily exceed dirty limit.
It mean we can see strange OOM.



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