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To: "Gilad Ben-Yossef" <gilad@benyossef.com>,
        "Andrew Morton" <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, "Chris Metcalf" <cmetcalf@tilera.com>,
        "Peter Zijlstra" <a.p.zijlstra@chello.nl>,
        "Frederic Weisbecker" <fweisbec@gmail.com>,
        "Russell King" <linux@arm.linux.org.uk>, linux-mm@kvack.org,
        "Pekka Enberg" <penberg@kernel.org>, "Matt Mackall" <mpm@selenic.com>,
        "Rik van Riel" <riel@redhat.com>, "Andi Kleen" <andi@firstfloor.org>,
        "Sasha Levin" <levinsasha928@gmail.com>, "Mel Gorman" <mel@csn.ul.ie>,
        "Alexander Viro" <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, "Avi Kivity" <avi@redhat.com>
Subject: Re: [PATCH v5 1/8] smp: Introduce a generic on_each_cpu_mask function
References: <1325499859-2262-1-git-send-email-gilad@benyossef.com>
 <1325499859-2262-2-git-send-email-gilad@benyossef.com>
 <20120103142624.faf46d77.akpm@linux-foundation.org>
Date: Thu, 05 Jan 2012 14:17:54 +0100
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From: "Michal Nazarewicz" <mina86@mina86.com>
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On Tue, 03 Jan 2012 23:26:24 +0100, Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon,  2 Jan 2012 12:24:12 +0200
> Gilad Ben-Yossef <gilad@benyossef.com> wrote:
>
>> on_each_cpu_mask calls a function on processors specified my cpumask,
>> which may include the local processor.

>> @@ -132,6 +139,15 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info)
>>  		local_irq_enable();		\
>>  		0;				\
>>  	})
>> +#define on_each_cpu_mask(mask, func, info, wait) \
>> +	do {						\
>> +		if (cpumask_test_cpu(0, (mask))) {	\
>> +			local_irq_disable();		\
>> +			(func)(info);			\
>> +			local_irq_enable();		\
>> +		}					\
>> +	} while (0)
>
> Why is the cpumask_test_cpu() call there?  It's hard to think of a
> reason why "mask" would specify any CPU other than "0" in a
> uniprocessor kernel.

It may specify none.  For instance, in drain_all_pages() case, if the
CPU has no pages on PCP lists, the mask will be empty and so the
cpumask_test_cpu() will return zero.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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