linux-kernel - Re: x86_64: Make sparsemem/vmemmap the default memory model

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Message-ID: <20071113204100.GB20167@lazybastard.org>
Date:	Tue, 13 Nov 2007 21:41:00 +0100
From:	Jörn Engel <joern@...fs.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Ray Lee <ray-lk@...rabbit.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mel@....ul.ie>, Andi Kleen <ak@...e.de>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: x86_64: Make sparsemem/vmemmap the default memory model

On Mon, 12 November 2007 20:41:10 -0800, Christoph Lameter wrote:
> On Mon, 12 Nov 2007, Ray Lee wrote:
> 
> > Discontig obviously needs to die. However, FlatMem is consistently
> > faster, averaging about 2.1% better overall for your numbers above. Is
> > the page allocator not, erm, a fast path, where that matters?
> > 
> > Order	Flat	Sparse	% diff
> > 0	639	641	0.3
> 
> IMHO Order 0 currently matters most and the difference is negligible 
> there.

Is it?  I am a bit concerned about the non-monotonic distribution.
Difference starts a near-0, grows to 4.4, drops to near-0, grows to 4.9,
drops to near-0.

Order   Flat    Sparse  % diff
0       639     641     0.3
1       567     593     4.4
2       679     692     1.9
3       763     781     2.3
4       961     962     0.1
5       1356    1392    2.6
6       2224    2336    4.8
7       4869    5074    4.0
8       12500   12732   1.8
9       27926   28165   0.8
10      58578   58682   0.2

Is there an explanation for this behaviour?  More to the point, could
repeated runs also return 4% difference for order-0?

Jörn

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