linux-kernel - Re: [patch] cpusets: do not allow TIF

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Date:	Wed, 06 Jun 2007 08:20:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen <ak@...e.de>,
	Christoph Lameter <clameter@...r.sgi.com>,
	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org
Subject: Re: [patch] cpusets: do not allow TIF_MEMDIE tasks to allocate
	globally

On Tue, 2007-06-05 at 15:39 -0700, David Rientjes wrote:
> Reverts git commit c596d9f320aaf30d28c1d793ff3a976dee1db8f5.
> 
> OOM-killed tasks, marked as TIF_MEMDIE, should not be able to access 
> memory outside its cpuset because it could potentially cause other 
> exclusive cpusets to OOM themselves.
> 
> Cc: Andi Kleen <ak@...e.de>
> Cc: Christoph Lameter <clameter@...r.sgi.com>
> Cc: Paul Jackson <pj@....com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  kernel/cpuset.c |    6 ------
>  1 files changed, 0 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -2431,12 +2431,6 @@ int __cpuset_zone_allowed_softwall(struct zone *z, gfp_t gfp_mask)
>  	might_sleep_if(!(gfp_mask & __GFP_HARDWALL));
>  	if (node_isset(node, current->mems_allowed))
>  		return 1;
> -	/*
> -	 * Allow tasks that have access to memory reserves because they have
> -	 * been OOM killed to get memory anywhere.
> -	 */
> -	if (unlikely(test_thread_flag(TIF_MEMDIE)))
> -		return 1;
>  	if (gfp_mask & __GFP_HARDWALL)	/* If hardwall request, stop here */
>  		return 0;
>  

This seems a little pointless, since cpuset_zone_allowed_softwall() is
only effective with ALLOC_CPUSET, and the ALLOC_NO_WATERMARKS
allocations opened up by TIF_MEMDIE don't use that.

Also I agree with Christoph's reasoning; this is not for the application
but for the system. Hence the cpuset does not get violated for the
application [ something I tried to argue before, glad Christoph now
agrees with me :-) ].

-
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