Re: [RFC] oom-kill: give the dying task a higher priority

[Minchan Kim]

On Mon, May 31, 2010 at 3:51 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Mon, 31 May 2010 15:09:41 +0900
> Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>
>> On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>> > On Mon, 31 May 2010 14:46:05 +0900
>> > Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>> >
>> >> On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
>> >> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>> >> > On Mon, 31 May 2010 14:01:03 +0900
>> >> > Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>> >> >
>> >> >> Hi, Kame.
>> >> >>
>> >> >> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
>> >> >> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>> >> >> > On Fri, 28 May 2010 13:48:26 -0300
>> >> >> > "Luis Claudio R. Goncalves" <lclaudio@xxxxxxxx> wrote:
>> >> >> >>
>> >> >> >> oom-killer: give the dying task rt priority (v3)
>> >> >> >>
>> >> >> >> Give the dying task RT priority so that it can be scheduled quickly and die,
>> >> >> >> freeing needed memory.
>> >> >> >>
>> >> >> >> Signed-off-by: Luis Claudio R. GonÃalves <lgoncalv@xxxxxxxxxx>
>> >> >> >>
>> >> >> >> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> >> >> >> index 84bbba2..2b0204f 100644
>> >> >> >> --- a/mm/oom_kill.c
>> >> >> >> +++ b/mm/oom_kill.c
>> >> >> >> @@ -266,6 +266,8 @@ static struct task_struct *select_bad_process(unsigned long *ppoints)
>> >> >> >> Â */
>> >> >> >> Âstatic void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >> >> Â{
>> >> >> >> + Â Â struct sched_param param;
>> >> >> >> +
>> >> >> >> Â Â Â if (is_global_init(p)) {
>> >> >> >> Â Â Â Â Â Â Â WARN_ON(1);
>> >> >> >> Â Â Â Â Â Â Â printk(KERN_WARNING "tried to kill init!\n");
>> >> >> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >> >> Â Â Â Â* exit() and clear out its resources quickly...
>> >> >> >> Â Â Â Â*/
>> >> >> >> Â Â Â p->time_slice = HZ;
>> >> >> >> + Â Â param.sched_priority = MAX_RT_PRIO-10;
>> >> >> >> + Â Â sched_setscheduler(p, SCHED_FIFO, &param);
>> >> >> >> Â Â Â set_tsk_thread_flag(p, TIF_MEMDIE);
>> >> >> >>
>> >> >> >
>> >> >> > BTW, how about the other threads which share mm_struct ?
>> >> >>
>> >> >> Could you elaborate your intention? :)
>> >> >>
>> >> >
>> >> > IIUC, the purpose of rising priority is to accerate dying thread to exit()
>> >> > for freeing memory AFAP. But to free memory, exit, all threads which share
>> >> > mm_struct should exit, too. I'm sorry if I miss something.
>> >>
>> >> How do we kill only some thread and what's the benefit of it?
>> >> I think when if some thread receives ÂKILL signal, the process include
>> >> the thread will be killed.
>> >>
>> > yes, so, if you want a _process_ die quickly, you have to acceralte the whole
>> > threads on a process. Acceralating a thread in a process is not big help.
>>
>> Yes.
>>
>> I see the code.
>> oom_kill_process is called by
>>
>> 1. mem_cgroup_out_of_memory
>> 2. __out_of_memory
>> 3. out_of_memory
>>
>>
>> (1,2) calls select_bad_process which select victim task in processes
>> by do_each_process.
>> But 3 isn't In case of ÂCONSTRAINT_MEMORY_POLICY, it kills current.
>> In only the case, couldn't we pass task of process, not one of thread?
>>
>
> Hmm, my point is that priority-acceralation is against a thread, not against a process.
> So, most of threads in memory-eater will not gain high priority even with this patch
> and works slowly.
> I have no objections to this patch. I just want to confirm the purpose. If this patch
> is for accelating exiting process by SIGKILL, it seems not enough.
> If an explanation as "acceralating all thread's priority in a process seems overkill"
> is given in changelog or comment, it's ok to me.

Okay. I got your point.
Kame's concern is proper.

Couldn't we raise priorities of whole threads of the task killed?

>
> Thanks,
> -Kame
>
>



-- 
Kind regards,
Minchan Kim
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