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

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Date:	Mon, 12 Nov 2007 20:27:34 -0800
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Christoph Lameter" <clameter@....com>
Cc:	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 Nov 12, 2007 7:42 PM, Christoph Lameter <clameter@....com> wrote:
> Ok here is the patch to remove DISCONTIG and FLATMEM
>
> x86_64: Make sparsemem/vmemmap the default memory model
>
> Use sparsemem as the only memory model for UP, SMP and NUMA.
> Measurements indicate that DISCONTIGMEM has a higher overhead
> than sparsemem. And FLATMEMs benefits are minimal. So I think its
> best to simply standardize on sparsemem.
>
> Results of page allocator tests (test can be had via git from slab git
> tree branch tests)
>
> Measurements in cycle counts. 1000 allocations were performed and then the
> average cycle count was calculated.
>
> Order   FlatMem Discontig       SparseMem
> 0         639     665             641
> 1         567     647             593
> 2         679     774             692
> 3         763     967             781
> 4         961    1501             962
> 5        1356    2344            1392
> 6        2224    3982            2336
> 7        4869    7225            5074
> 8       12500   14048           12732
> 9       27926   28223           28165
> 10      58578   58714           58682

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
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
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