linux-kernel - Re: [PATCH 2/2] memcg: coalescing charge by percpu (Oct/9)

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Date:	Sun, 11 Oct 2009 11:37:35 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	h-shimamoto@...jp.nec.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] memcg: coalescing charge by percpu (Oct/9)

Andrew Morton wrote:
> On Fri, 9 Oct 2009 17:01:05 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
>> +static void drain_all_stock_async(void)
>> +{
>> +	int cpu;
>> +	/* This function is for scheduling "drain" in asynchronous way.
>> +	 * The result of "drain" is not directly handled by callers. Then,
>> +	 * if someone is calling drain, we don't have to call drain more.
>> +	 * Anyway, work_pending() will catch if there is a race. We just do
>> +	 * loose check here.
>> +	 */
>> +	if (atomic_read(&memcg_drain_count))
>> +		return;
>> +	/* Notify other cpus that system-wide "drain" is running */
>> +	atomic_inc(&memcg_drain_count);
>> +	get_online_cpus();
>> +	for_each_online_cpu(cpu) {
>> +		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
>> +		if (work_pending(&stock->work))
>> +			continue;
>> +		INIT_WORK(&stock->work, drain_local_stock);
>> +		schedule_work_on(cpu, &stock->work);
>> +	}
>> + 	put_online_cpus();
>> +	atomic_dec(&memcg_drain_count);
>> +	/* We don't wait for flush_work */
>> +}
>
> It's unusual to run INIT_WORK() each time we use a work_struct.
> Usually we will run INIT_WORK a single time, then just repeatedly use
> that structure.  Because after the work has completed, it is still in a
> ready-to-use state.
>
> Running INIT_WORK() repeatedly against the same work_struct adds a risk
> that we'll scribble on an in-use work_struct, which would make a big
> mess.
>
Ah, ok. I'll prepare a fix. (And I think atomic_dec/inc placement is not
very good....I'll do total review, again.)

Thank you for review.

Regards,
-Kame


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