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

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Message-ID: <alpine.DEB.1.10.0904010948120.7643@qirst.com>
Date:	Wed, 1 Apr 2009 09:49:25 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	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, matthew@....cx,
	grundler@...isc-linux.org, takata@...ux-m32r.org,
	benh@...nel.crashing.org, rth@...ddle.net,
	ink@...assic.park.msu.ru, heiko.carstens@...ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH UPDATED] percpu: use dynamic percpu allocator as the
 default percpu allocator

On Wed, 1 Apr 2009, Tejun Heo wrote:

> > 1. Lot of unnecessary use of __read_mostly for local static variables that
> > are not on the hotpath. Patch follows in this message.
>
> Hmmm... Those are basically read-only vars once initialization is
> complete.  IIUC, __read_mostly just puts the tagged variables into a
> separate segment so that they don't have to worry about cacheline
> bouncing.  Is there any reason to remove __read_mostly?  Or is it just
> that it's mostly superflous?

Yes its better for the variables to be all together if its not on hot
cache paths. And its better to keep the __read_mostly segment reserved for
frequently accessed variables.
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