linux-kernel - Re: [PATCH UPDATED] percpu: use dynamic percpu allocator as the default percpu allocator

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Message-ID: <20090401201236.GK8014@parisc-linux.org>
Date:	Wed, 1 Apr 2009 14:12:37 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Christoph Lameter <cl@...ux.com>,
	Tejun Heo <tj@...nel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	Paul Mundt <lethal@...ux-sh.org>, rmk@....linux.org.uk,
	starvik@...s.com, ralf@...ux-mips.org, davem@...emloft.net,
	cooloney@...nel.org, kyle@...artin.ca, grundler@...isc-linux.org,
	takata@...ux-m32r.org, benh@...nel.crashing.org, rth@...ddle.net,
	ink@...assic.park.msu.ru, heiko.carstens@...ibm.com,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH UPDATED] percpu: use dynamic percpu allocator as the default percpu allocator

On Wed, Apr 01, 2009 at 12:39:46PM -0700, Linus Torvalds wrote:
> The thing is, things like "read_mostly" or "access_rarely" may talk about 
> how we access those individual variables, but you're missing a _huge_ 
> chunk of the puzzle if you ignore the _correlations_ of those accesses 
> with accesses to other variables.
> 
> The thign is, if you have variables 'a' and 'b', and they are always 
> accessed together, then it's probably worth it to put them in the same 
> cacheline.

If you've got two global variables that are generally accessed together,
they should probably be `annotated' as such by putting them in a struct.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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