linux-kernel - Re: [patch -mm] mm: slab allocate memory section nodemask for large systems

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Message-ID: <20091118183523.GA7793@us.ibm.com>
Date:	Wed, 18 Nov 2009 10:35:24 -0800
From:	Gary Hade <garyhade@...ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gary Hade <garyhade@...ibm.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Alex Chiang <achiang@...com>, linux-kernel@...r.kernel.org
Subject: Re: [patch -mm] mm: slab allocate memory section nodemask for
	large systems

Hi David,

On Tue, Nov 17, 2009 at 04:19:30PM -0800, David Rientjes wrote:
> Nodemasks should not be allocated on the stack for large systems (when it
> is larger than 256 bytes) since there is a threat of overflow.
> 
> This patch causes the unregister_mem_sect_under_nodes() nodemask to be
> allocated on the stack for smaller systems and be allocated by slab for
> larger systems.

I notice that there are many other functions that always allocate
nodemask_t objects on the stack.  In addition to several that add
a single instance to the stack, cpuset_attach() in kernel/cpuset.c
adds 2 instances and all that are created by using SYSCALL_DEFINE4()
in mm/mempolicy.c add 3 instances.  Are there plans to correct the
other functions as well or is there something about
unregister_mem_sect_under_nodes() that makes it more likely to
cause stack overflows than the others?

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc

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