linux-kernel - Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush

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Date:	Sun, 01 Jan 2012 14:41:30 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Gilad Ben-Yossef <gilad@...yossef.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,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, apkm@...ux-foundation.org
Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush

On 11/23/2011 08:23 AM, Pekka Enberg wrote:
> On Tue, 22 Nov 2011, Gilad Ben-Yossef wrote:
>> static void flush_all(struct kmem_cache *s)
>> {
>> -    on_each_cpu(flush_cpu_slab, s, 1);
>> +    cpumask_var_t cpus;
>> +    struct kmem_cache_cpu *c;
>> +    int cpu;
>> +
>> +    if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC))) {
>
> __GFP_NOWARN too maybe?
>
>> +        for_each_online_cpu(cpu) {
>> +            c = per_cpu_ptr(s->cpu_slab, cpu);
>> +            if (c->page)
>> +                cpumask_set_cpu(cpu, cpus);
>> +        }
>> +        on_each_cpu_mask(cpus, flush_cpu_slab, s, 1);
>> +        free_cpumask_var(cpus);
>> +    } else
>> +        on_each_cpu(flush_cpu_slab, s, 1);
>> }
>

Since this seems to be a common pattern, how about:

   zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC);
   ...
   free_cpumask_var(cpus);

The long-named function at the top of the block either returns a newly
allocated zeroed cpumask, or a static cpumask with all online cpus set. 
The code in the middle is only allowed to set bits in the cpumask
(should be the common usage).  free_cpumask_var() needs to check whether
the freed object is the static variable.

-- 
error compiling committee.c: too many arguments to function

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