linux-kernel - Re: [PATCH] cpuset: fix allocating page cache/slab object on the unallowed node when memory spread is set

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Message-ID: <4989606F.9030804@cn.fujitsu.com>
Date:	Wed, 04 Feb 2009 17:31:27 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	nickpiggin@...oo.com.au
Subject: Re: [PATCH] cpuset: fix allocating page cache/slab object on the
 unallowed node when memory spread is set

on 2009-2-4 6:49 Paul Menage wrote:
> On Tue, Feb 3, 2009 at 2:16 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>> On Tue, 03 Feb 2009 11:25:25 +0800
>> Miao Xie <miaox@...fujitsu.com> wrote:
[snip]
>>
>> I wasn't able to find out where the setting of init'smems_allowed
>> happens, after a bit of grepping and hunting.  It should be done within
>> INIT_TASK, but isn't.
>>
>> Still, kthreadd is reliably parented by swapper, and there shold be no
>> need to alter its mems_allowed.
>>
>> Similarly, what was the reason for setting current->mems_allowed in
>> kernel_init()?  That also should be unneeded.
>>
>> Finally, I've somewhat lost track of where we are with this patch.
>> Paul, do you see any other remaining issues?
> 
> AFAICS this patch still has a race between a thread reading its
> mems_allowed, and another thread updating it. The current architecture
> of having task->mems_allowed be only updatable by current was PaulJ's
> code originally, and I'm a bit loathe to touch it. But if we're going
> to, we'll need at the minimum to add a lock for any code that touches
> current->mems_allowed.

Agree! But mems_allowed is touched in the module of memory management
in general, adding a lock to protect mems_allowed may lead to performance
regression.

> 
> Paul
> 
> 
> 


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