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

[KAMEZAWA Hiroyuki]

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  CONSTRAINT_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.

Thanks,
-Kame

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