linux-kernel - Re: [uml-devel] BUG: soft lockup for a user mode linux image

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Date:	Fri, 11 Oct 2013 17:05:34 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	Richard Weinberger <richard@....at>, Jan Kara <jack@...e.cz>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	UML devel <user-mode-linux-devel@...ts.sourceforge.net>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	hannes@...xchg.org, darrick.wong@...cle.com,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [uml-devel] BUG: soft lockup for a user mode linux image

On Fri, Oct 11, 2013 at 04:57:01PM +0800, Fengguang Wu wrote:
> On Fri, Oct 11, 2013 at 10:42:19AM +0200, Toralf Förster wrote:
> > yeah, now the picture becomes more clear
> > ...
> > net.core.warnings = 0                                                                         [ ok ]
> > ick: pause : -717
> >                  ick : min_pause : -177
> >                                    ick : max_pause : -717
> >                                                      ick: pages_dirtied : 14
> >                                                                             ick: task_ratelimit: 0
> 
> Great and thanks! So it's the max pause calculation went wrong.

However I still suspect this is not the main reason for the soft
lockup. Because schedule_timeout() will directly return on negative
timeout. So yes, we have encountered some negative pauses, however
we still need to fix the huge dirtied pages problem which should be
more fundamental. 

Thanks,
Fengguang
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