linux-kernel - Re: [PATCH 1/2] scalable rw

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Message-Id: <20070512111100.86ae13f6.akpm@linux-foundation.org>
Date:	Sat, 12 May 2007 11:11:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 1/2] scalable rw_mutex

On Sat, 12 May 2007 11:06:24 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> We could put a cpumask in percpu_counter, initialise it to
> cpu_possible_map.  Then, those callsites which have hotplug notifiers can
> call into new percpu_counter functions which clear and set bits in that
> cpumask and which drain percpu_counter.counts[cpu] into
> percpu_counter.count.
> 
> And percpu_counter_sum() gets taught to do for_each_cpu_mask(fbc->cpumask).

Perhaps we could have a single cpu hotplug notifier in the percpu_counter
library.  Add register/deregister functions to the percpu_counter API so
that all percpu_counters in the machine can be linked together.

One _could_ just register and deregister the counters in
percpu_counter_init() and percpu_counter_destroy(), but perhaps that
wouldn't suit all callers, dunno.

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