linux-kernel - Re: [PATCH v2]mm/oom-kill: direct hardware access processes should get bonus

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Date:	Wed, 10 Nov 2010 22:48:16 +0800
From:	"Figo.zhang" <figo1802@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2]mm/oom-kill: direct hardware access processes should
 get bonus

On Tue, 2010-11-09 at 13:16 -0800, David Rientjes wrote:
> On Tue, 9 Nov 2010, Figo.zhang wrote:
> 
> >  
> > the victim should not directly access hardware devices like Xorg server,
> > because the hardware could be left in an unpredictable state, although 
> > user-application can set /proc/pid/oom_score_adj to protect it. so i think
> > those processes should get 3% bonus for protection.
> > 
> 
> The logic here is wrong: if killing these tasks can leave hardware in an 
> unpredictable state (and that state is presumably harmful), then they 
> should be completely immune from oom killing since you're still leaving 
> them exposed here to be killed.

we let the processes with hardware access get bonus for protection. the
goal is not select them to be killed as possible.


> 
> So the question that needs to be answered is: why do these threads deserve 
> to use 3% more memory (not >4%) than others without getting killed?  If 
> there was some evidence that these threads have a certain quantity of 
> memory they require as a fundamental attribute of CAP_SYS_RAWIO, then I 
> have no objection, but that's going to be expressed in a memory quantity 
> not a percentage as you have here.
> 
> The CAP_SYS_ADMIN heuristic has a background: it is used in the oom killer 
> because we have used the same 3% in __vm_enough_memory() for a long time 
> and we want consistency amongst the heuristics.  Adding additional bonuses 
> with arbitrary values like 3% of memory for things like CAP_SYS_RAWIO 
> makes the heuristic less predictable and moves us back toward the old 
> heuristic which was almost entirely arbitrary.


yes, i think it is be better those processes which be protection maybe
divided the badness score by 4, like old heuristic.




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