linux-kernel - Re: [PATCH 0/5] make slab gfp fair

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Message-ID: <Pine.LNX.4.64.0705171220120.3043@schroedinger.engr.sgi.com>
Date:	Thu, 17 May 2007 12:24:54 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Thomas Graf <tgraf@...g.ch>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/5] make slab gfp fair

On Thu, 17 May 2007, Peter Zijlstra wrote:

> The proposed patch doesn't change how the kernel functions at this
> point; it just enforces an existing rule better.

Well I'd say it controls the allocation failures. And that only works if 
one can consider the system having a single zone.

Lets say the system has two cpusets A and B. A allocs from node 1 and B 
allocs from node 2. Two processes one in A and one in B run on the same 
processor.

Node 1 gets very low in memory so your patch kicks in and sets up the 
global memory emergency situation with the reserve slab.

Now the process in B will either fail although it has plenty of memory on 
node 2.

Or it may just clear the emergency slab and then the next critical alloc 
of the process in A that is low on memory will fail.

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