linux-kernel - Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations

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Message-Id: <200806131038.12987.rusty@rustcorp.com.au>
Date:	Fri, 13 Jun 2008 10:38:12 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Martin Peschke <mp3@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Travis <travis@....com>
Subject: Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations

On Friday 13 June 2008 03:19:51 Christoph Lameter wrote:
> Populating the per cpu areas on demand is a good thing especially for
> configurations with a large number of processors. If we really go to 
> support 4k processor by default then we need to allocate the smallest
> amount of per cpu structures necessary.  Maybe ACPI or so can tell us how 
> many processors are possible and we only allocate those. But it would be
> best if the percpu structures are only allocated for actually active
> processors.

cpu_possible_map should definitely be minimal, but your point is well made: 
dynamic percpu could actually cut memory allocation.  If we go for a hybrid 
scheme where static percpu is always allocated from the initial chunk, 
however, we still need the current pessimistic overallocation.

Mike's a clever guy, I'm sure he'll think of something :)
Rusty.
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