linux-kernel - Re: [PATCH] Document huge memory/cache overhead of memory controller in Kconfig

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Message-Id: <200802211535.38932.nickpiggin@yahoo.com.au>
Date:	Thu, 21 Feb 2008 15:35:38 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	balbir@...ux.vnet.ibm.com
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...l.org, torvalds@...l.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Document huge memory/cache overhead of memory controller in Kconfig

On Wednesday 20 February 2008 23:52, Balbir Singh wrote:
> Andi Kleen wrote:
> > Document huge memory/cache overhead of memory controller in Kconfig
> >
> > I was a little surprised that 2.6.25-rc* increased struct page for the
> > memory controller.  At least on many x86-64 machines it will not fit into
> > a single cache line now anymore and also costs considerable amounts of
> > RAM.
>
> The size of struct page earlier was 56 bytes on x86_64 and with 64 bytes it
> won't fit into the cacheline anymore? Please also look at
> http://lwn.net/Articles/234974/

BTW. We'll probably want to increase the width of some counters
in struct page at some point for 64-bit, so then it really will
go over with the memory controller!

Actually, an external data structure is a pretty good idea. We
could probably do it easily with a radix tree (pfn->memory
controller). And that might be a better option for distros.

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