linux-kernel - Re: [PATCH v6 7/8] mm: only IPI CPUs to drain local pages if they exist

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Date:	Tue, 10 Jan 2012 14:43:21 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
	Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v6 7/8] mm: only IPI CPUs to drain local pages if they exist

2012/1/9 Michal Nazarewicz <mina86@...a86.com>:
> On Mon, 09 Jan 2012 17:35:26 +0100, Christoph Lameter <cl@...ux.com> wrote:
>
>> On Sun, 8 Jan 2012, Gilad Ben-Yossef wrote:
>>
>>> @@ -67,6 +67,14 @@ DEFINE_PER_CPU(int, numa_node);
>>>  EXPORT_PER_CPU_SYMBOL(numa_node);
>>>  #endif
>>>
>>> +/*
>>> + * A global cpumask of CPUs with per-cpu pages that gets
>>> + * recomputed on each drain. We use a global cpumask
>>> + * here to avoid allocation on direct reclaim code path
>>> + * for CONFIG_CPUMASK_OFFSTACK=y
>>> + */
>>> +static cpumask_var_t cpus_with_pcps;
>>
>>
>> Move the static definition into drain_all_pages()?
>
>
> This is initialised in setup_per_cpu_pageset() so it needs to be file
> scoped.

Yes. The cpumask_var_t abstraction is convenient and all but it does
make the allocation
very non obvious when it does not happen in proximity to the variable
use - it doesn't *look* like
a pointer. "syntactic sugar causes cancer of the semicolon" and all that.

Gilad



-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
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"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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