Re: [PATCH 2/4] oom: kill younger process first

[Minchan Kim]

Hi Kame,

On Thu, May 12, 2011 at 9:52 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Tue, 10 May 2011 17:15:01 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
>
>> This patch introduces do_each_thread_reverse() and
>> select_bad_process() uses it. The benefits are two,
>> 1) oom-killer can kill younger process than older if
>> they have a same oom score. Usually younger process
>> is less important. 2) younger task often have PF_EXITING
>> because shell script makes a lot of short lived processes.
>> Reverse order search can detect it faster.
>>
>> Reported-by: CAI Qian <caiqian@xxxxxxxxxx>
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>
> IIUC, for_each_thread() can be called under rcu_read_lock() but
> for_each_thread_reverse() must be under tasklist_lock.

Just out of curiosity.
You mentioned it when I sent forkbomb killer patch. :)
>From at that time, I can't understand why we need holding
tasklist_lock not rcu_read_lock. Sorry for the dumb question.

At present, it seems that someone uses tasklist_lock and others uses
rcu_read_lock. But I can't find any rule for that.

Could you elaborate it, please?
Doesn't it need document about it?

-- 
Kind regards,
Minchan Kim
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