linux-kernel - Re: [PATCH v7 2/2] mm: make lru_add_drain

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Message-ID: <520AC215.4050803@tilera.com>
Date:	Tue, 13 Aug 2013 19:32:37 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH v7 2/2] mm: make lru_add_drain_all() selective

On 8/13/2013 7:29 PM, Tejun Heo wrote:
> Hello,
>
> On Tue, Aug 13, 2013 at 06:53:32PM -0400, Chris Metcalf wrote:
>>  int lru_add_drain_all(void)
>>  {
>> -	return schedule_on_each_cpu(lru_add_drain_per_cpu);
>> +	return schedule_on_each_cpu_cond(lru_add_drain_per_cpu,
>> +					 lru_add_drain_cond, NULL);
> It won't nest and doing it simultaneously won't buy anything, right?

Correct on both counts, I think.

> Wouldn't it be better to protect it with a mutex and define all
> necessary resources statically (yeah, cpumask is pain in the ass and I
> think we should un-deprecate cpumask_t for static use cases)?  Then,
> there'd be no allocation to worry about on the path.

If allocation is a real problem on this path, I think this is probably
OK, though I don't want to speak for Andrew.  You could just guard it
with a trylock and any caller that tried to start it while it was
locked could just return happy that it was going on.

I'll put out a version that does that and see how that looks
for comparison's sake.

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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