linux-kernel - Re: [QUICKLIST 4/6] x86

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Message-ID: <20070314194941.GA21862@skynet.ie>
Date:	Wed, 14 Mar 2007 19:49:41 +0000
From:	mel@...net.ie (Mel Gorman)
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org, ak@...e.com,
	linux-ia64@...r.kernel.org, holt@....com, mpm@...enic.com
Subject: Re: [QUICKLIST 4/6] x86_64: Single Quicklist

On (11/03/07 09:44), Christoph Lameter didst pronounce:
> On Sun, 11 Mar 2007, Andi Kleen wrote:
> 
> > This and i386 version are ok to me, although it might be better to just
> > finish __GFP_ZERO support to do this.
> 
> This would not work for pgds on i386 and x86_64
> 
> GFP_ZERO support the way I have done it in the past would mean another set 
> of buddy lists in the page allocator and another issue with fragmentation. 
> So I have stayed away from it although patches exist in my archives (See 
> my ftp.kernel.org archive).

I haven't checked this in a while but when we experimented with keeping
zero'd pages on separate lists before, the performance sucked. I haven't
looked at it in a *long* time though.

> 
> Maybe we could implemento limited GFP_ZERO support by just keeping an 
> additional per cpu list of pages?

I imagine that adding an additional per-cpu list will not be welcome.

> The issue with that one is that a page
> may grow cold on that list.

And that growing cold appeared to hurt before. It could be checked out
again though. The anti-fragmentation breaks out the buddy lists already
and has the ability to search the per-cpu lists for pages of an
appropriate type.

I'll try and find an hour or two to hack something together to see what
it looks like but I suspect it'll still be a performance loss. At least
then though, we can see if quicklists are a better plan or not.

> One usually want the page to be hot in the 
> cache when it is allocated. This is different for page table pages. Page 
> table pages are typically sparsely accessed.
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-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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