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SubjectRe: [PATCH 2/2] memcg: coalescing charge by percpu (Oct/9)
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Andrew Morton wrote:
> On Fri, 9 Oct 2009 17:01:05 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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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