linux-kernel - Re: The performance and behaviour of the anti-fragmentation related patches

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Date:	Fri, 2 Mar 2007 09:23:49 -0800 (PST)
From:	Christoph Lameter <clameter@...r.sgi.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@...net.ie>,
	npiggin@...e.de, mingo@...e.hu, jschopp@...tin.ibm.com,
	arjan@...radead.org, torvalds@...ux-foundation.org,
	mbligh@...igh.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: The performance and behaviour of the anti-fragmentation related
 patches

On Fri, 2 Mar 2007, Andrew Morton wrote:

> > Linux is *not* happy on 256GB systems.  Even on some 32GB systems
> > the swappiness setting *needs* to be tweaked before Linux will even
> > run in a reasonable way.
> 
> Please send testcases.

It is not happy if you put 256GB into one zone. We are fine with 1k nodes 
with 8GB each and a 16k page size (which reduces the number of 
page_structs to manage by a fourth). So the total memory is 8TB which is 
significantly larger than 256GB.

If we do this node/zone merging and reassign MAX_ORDER blocks to virtual 
node/zones for containers (with their own LRU etc) then this would also 
reduce the number of page_structs on the list and may make things a bit 
easier.

We would then produce the same effect as the partitioning via NUMA nodes 
on our 8TB boxes. However, then you still have a bandwidth issue since 
your 256 likely only has a single bus and all memory traffic for the 
node/zones has to go through this single bottleneck. That bottleneck does 
not exist on NUMA machines.

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