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

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

[Luis Claudio R. Goncalves]

Hello,

Could you please review this patch?

The idea behind it is quite simple: give the dying task a higher priority
so that it can be scheduled sooner and die to free memory.


oom-kill: give the dying task a higher priority

In a system under heavy load it was observed that even after the
oom-killer selects a task to die, the task may take a long time to die.

Right before sending a SIGKILL to the selected task the oom-killer
increases the task priority so that it can exit quickly, freeing memory.
That is accomplished by:

        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);

It sounds plausible giving the dying task an even higher priority to be
sure it will be scheduled sooner and free the desired memory.

Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index b68e802..8047309 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
  */
 static void __oom_kill_task(struct task_struct *p, int verbose)
 {
+	struct sched_param param;
+
 	if (is_global_init(p)) {
 		WARN_ON(1);
 		printk(KERN_WARNING "tried to kill init!\n");
@@ -413,6 +415,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
 	 */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);
+	param.sched_priority = MAX_RT_PRIO-1;
+	sched_setscheduler(p, SCHED_FIFO, &param);
 
 	force_sig(SIGKILL, p);
 }


Thanks,
Luis
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Oleg Nesterov]

On 05/27, Luis Claudio R. Goncalves wrote:
>
> It sounds plausible giving the dying task an even higher priority to be
> sure it will be scheduled sooner and free the desired memory.

As usual, I can't really comment the changes in oom logic, just minor
nits...

> @@ -413,6 +415,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> +	param.sched_priority = MAX_RT_PRIO-1;
> +	sched_setscheduler(p, SCHED_FIFO, &param);
>
>  	force_sig(SIGKILL, p);

Probably sched_setscheduler_nocheck() makes more sense.

Minor, but perhaps it would be a bit better to send SIGKILL first,
then raise its prio.

Oleg.

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

[KOSAKI Motohiro]

Hi Luis,

> On 05/27, Luis Claudio R. Goncalves wrote:
> >
> > It sounds plausible giving the dying task an even higher priority to be
> > sure it will be scheduled sooner and free the desired memory.
> 
> As usual, I can't really comment the changes in oom logic, just minor
> nits...
> 
> > @@ -413,6 +415,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >  	 */
> >  	p->rt.time_slice = HZ;
> >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > +	param.sched_priority = MAX_RT_PRIO-1;
> > +	sched_setscheduler(p, SCHED_FIFO, &param);
> >
> >  	force_sig(SIGKILL, p);
> 
> Probably sched_setscheduler_nocheck() makes more sense.
> 
> Minor, but perhaps it would be a bit better to send SIGKILL first,
> then raise its prio.

I have no objection too. but I don't think Oleg's pointed thing is minor.
Please send updated patch.

Thanks.


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

[Luis Claudio R. Goncalves]

On Fri, May 28, 2010 at 11:54:07AM +0900, KOSAKI Motohiro wrote:
| Hi Luis,
| 
| > On 05/27, Luis Claudio R. Goncalves wrote:
| > >
| > > It sounds plausible giving the dying task an even higher priority to be
| > > sure it will be scheduled sooner and free the desired memory.
| > 
| > As usual, I can't really comment the changes in oom logic, just minor
| > nits...
| > 
| > > @@ -413,6 +415,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
| > >  	 */
| > >  	p->rt.time_slice = HZ;
| > >  	set_tsk_thread_flag(p, TIF_MEMDIE);
| > > +	param.sched_priority = MAX_RT_PRIO-1;
| > > +	sched_setscheduler(p, SCHED_FIFO, &param);
| > >
| > >  	force_sig(SIGKILL, p);
| > 
| > Probably sched_setscheduler_nocheck() makes more sense.
| > 
| > Minor, but perhaps it would be a bit better to send SIGKILL first,
| > then raise its prio.
| 
| I have no objection too. but I don't think Oleg's pointed thing is minor.
| Please send updated patch.
| 
| Thanks.

This version of the patch addresses the suggestions from Oleg Nesterov and
Kosaki Motohiro.

Thanks again for reviewing the patch.

oom-kill: give the dying task a higher priority (v2)

In a system under heavy load it was observed that even after the
oom-killer selects a task to die, the task may take a long time to die.

Right before sending a SIGKILL to the task selected by the oom-killer
this task has it's priority increased so that it can exit() exit soon,
freeing memory. That is accomplished by:

        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);

It sounds plausible giving the dying task an even higher priority to be
sure it will be scheduled sooner and free the desired memory. Oleg Nesterov
pointed out it would be interesting sending the signal before increasing
the task priority.

Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index b68e802..d352b3e 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
  */
 static void __oom_kill_task(struct task_struct *p, int verbose)
 {
+	struct sched_param param;
+
 	if (is_global_init(p)) {
 		WARN_ON(1);
 		printk(KERN_WARNING "tried to kill init!\n");
@@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
 	 */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);
-
 	force_sig(SIGKILL, p);
+	param.sched_priority = MAX_RT_PRIO-1;
+	sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
 }
 
 static int oom_kill_task(struct task_struct *p)
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Balbir Singh]

* Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:

> @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>   */
>  static void __oom_kill_task(struct task_struct *p, int verbose)
>  {
> +	struct sched_param param;
> +
>  	if (is_global_init(p)) {
>  		WARN_ON(1);
>  		printk(KERN_WARNING "tried to kill init!\n");
> @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> -
>  	force_sig(SIGKILL, p);
> +	param.sched_priority = MAX_RT_PRIO-1;
> +	sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
>  }
>

I would like to understand the visible benefits of this patch. Have
you seen an OOM kill tasked really get bogged down. Should this task
really be competing with other important tasks for run time?

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	Balbir

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

[KOSAKI Motohiro]

> * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
> 
> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> >   */
> >  static void __oom_kill_task(struct task_struct *p, int verbose)
> >  {
> > +	struct sched_param param;
> > +
> >  	if (is_global_init(p)) {
> >  		WARN_ON(1);
> >  		printk(KERN_WARNING "tried to kill init!\n");
> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >  	 */
> >  	p->rt.time_slice = HZ;
> >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > -
> >  	force_sig(SIGKILL, p);
> > +	param.sched_priority = MAX_RT_PRIO-1;
> > +	sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> >  }
> >
> 
> I would like to understand the visible benefits of this patch. Have
> you seen an OOM kill tasked really get bogged down. Should this task
> really be competing with other important tasks for run time?

What you mean important? Until OOM victim task exit completely, the system have no memory.
all of important task can't do anything.

In almost kernel subsystems, automatically priority boost is really bad idea because
it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
was alread broken by memory starvation.

That's the reason I acked it.


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

[Minchan Kim]

Hi, Kosaki.

On Fri, May 28, 2010 at 1:46 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
>>
>> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>> >   */
>> >  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >  {
>> > +   struct sched_param param;
>> > +
>> >     if (is_global_init(p)) {
>> >             WARN_ON(1);
>> >             printk(KERN_WARNING "tried to kill init!\n");
>> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >      */
>> >     p->rt.time_slice = HZ;
>> >     set_tsk_thread_flag(p, TIF_MEMDIE);
>> > -
>> >     force_sig(SIGKILL, p);
>> > +   param.sched_priority = MAX_RT_PRIO-1;
>> > +   sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
>> >  }
>> >
>>
>> I would like to understand the visible benefits of this patch. Have
>> you seen an OOM kill tasked really get bogged down. Should this task
>> really be competing with other important tasks for run time?
>
> What you mean important? Until OOM victim task exit completely, the system have no memory.
> all of important task can't do anything.
>
> In almost kernel subsystems, automatically priority boost is really bad idea because
> it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
> was alread broken by memory starvation.

Yes or No.

IMHO, normally RT tasks shouldn't use dynamic allocation(ie,
non-deterministic functions or system calls) in place which is needed
deterministic. So memory starvation might not break real-time
deterministic.


>
> That's the reason I acked it.

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

[KOSAKI Motohiro]

Hi

> Hi, Kosaki.
> 
> On Fri, May 28, 2010 at 1:46 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> >> * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
> >>
> >> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> >> > A  */
> >> > A static void __oom_kill_task(struct task_struct *p, int verbose)
> >> > A {
> >> > + A  struct sched_param param;
> >> > +
> >> > A  A  if (is_global_init(p)) {
> >> > A  A  A  A  A  A  WARN_ON(1);
> >> > A  A  A  A  A  A  printk(KERN_WARNING "tried to kill init!\n");
> >> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >> > A  A  A */
> >> > A  A  p->rt.time_slice = HZ;
> >> > A  A  set_tsk_thread_flag(p, TIF_MEMDIE);
> >> > -
> >> > A  A  force_sig(SIGKILL, p);
> >> > + A  param.sched_priority = MAX_RT_PRIO-1;
> >> > + A  sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> >> > A }
> >> >
> >>
> >> I would like to understand the visible benefits of this patch. Have
> >> you seen an OOM kill tasked really get bogged down. Should this task
> >> really be competing with other important tasks for run time?
> >
> > What you mean important? Until OOM victim task exit completely, the system have no memory.
> > all of important task can't do anything.
> >
> > In almost kernel subsystems, automatically priority boost is really bad idea because
> > it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
> > was alread broken by memory starvation.
> 
> Yes or No.
> 
> IMHO, normally RT tasks shouldn't use dynamic allocation(ie,
> non-deterministic functions or system calls) in place which is needed
> deterministic. So memory starvation might not break real-time
> deterministic.

I think It's impossible. Normally RT task use mlock and it prevent almost page
allocation. but every syscall internally call kmalloc(). They can't avoid
it practically.

How do you perfectly avoid dynamic allocation?


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

[Minchan Kim]

On Fri, May 28, 2010 at 2:39 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi
>
>> Hi, Kosaki.
>>
>> On Fri, May 28, 2010 at 1:46 PM, KOSAKI Motohiro
>> <kosaki.motohiro@jp.fujitsu.com> wrote:
>> >> * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
>> >>
>> >> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>> >> >   */
>> >> >  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >  {
>> >> > +   struct sched_param param;
>> >> > +
>> >> >     if (is_global_init(p)) {
>> >> >             WARN_ON(1);
>> >> >             printk(KERN_WARNING "tried to kill init!\n");
>> >> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >      */
>> >> >     p->rt.time_slice = HZ;
>> >> >     set_tsk_thread_flag(p, TIF_MEMDIE);
>> >> > -
>> >> >     force_sig(SIGKILL, p);
>> >> > +   param.sched_priority = MAX_RT_PRIO-1;
>> >> > +   sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
>> >> >  }
>> >> >
>> >>
>> >> I would like to understand the visible benefits of this patch. Have
>> >> you seen an OOM kill tasked really get bogged down. Should this task
>> >> really be competing with other important tasks for run time?
>> >
>> > What you mean important? Until OOM victim task exit completely, the system have no memory.
>> > all of important task can't do anything.
>> >
>> > In almost kernel subsystems, automatically priority boost is really bad idea because
>> > it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
>> > was alread broken by memory starvation.
>>
>> Yes or No.
>>
>> IMHO, normally RT tasks shouldn't use dynamic allocation(ie,
>> non-deterministic functions or system calls) in place which is needed
>> deterministic. So memory starvation might not break real-time
>> deterministic.
>
> I think It's impossible. Normally RT task use mlock and it prevent almost page
> allocation. but every syscall internally call kmalloc(). They can't avoid
> it practically.
>
> How do you perfectly avoid dynamic allocation?

RT Task

void non-RT-function()
{
   system call();
   buffer = malloc();
   memset(buffer);
}
/*
 * We make sure this function must be executed in some millisecond
 */
void RT-function()
{
   some calculation(); <- This doesn't have no dynamic characteristic
}
int main()
{
   non-RT-function();
   /* This function make sure RT-function cannot preempt by others */
   set_RT_max_high_priority();
   RT-function A();
   set_normal_priority();
   non-RT-function();
}

We don't want realtime in whole function of the task. What we want is
just RT-function A.
Of course, current Linux cannot make perfectly sure RT-functionA can
not preempt by others.
That's because some interrupt or exception happen. But RT-function A
doesn't related to any dynamic characteristic. What can justify to
preempt RT-function A by other processes?


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

[KOSAKI Motohiro]

> RT Task
> 
> void non-RT-function()
> {
>    system call();
>    buffer = malloc();
>    memset(buffer);
> }
> /*
>  * We make sure this function must be executed in some millisecond
>  */
> void RT-function()
> {
>    some calculation(); <- This doesn't have no dynamic characteristic
> }
> int main()
> {
>    non-RT-function();
>    /* This function make sure RT-function cannot preempt by others */
>    set_RT_max_high_priority();
>    RT-function A();
>    set_normal_priority();
>    non-RT-function();
> }
> 
> We don't want realtime in whole function of the task. What we want is
> just RT-function A.
> Of course, current Linux cannot make perfectly sure RT-functionA can
> not preempt by others.
> That's because some interrupt or exception happen. But RT-function A
> doesn't related to any dynamic characteristic. What can justify to
> preempt RT-function A by other processes?

As far as my observation, RT-function always have some syscall. because pure
calculation doesn't need deterministic guarantee. But _if_ you are really
using such priority design. I'm ok maximum NonRT priority instead maximum
RT priority too.

Luis, NonRT high priority break your use case? and if yes, can you please
explain the reason?



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

[Minchan Kim]

On Fri, May 28, 2010 at 2:59 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> RT Task
>>
>> void non-RT-function()
>> {
>>    system call();
>>    buffer = malloc();
>>    memset(buffer);
>> }
>> /*
>>  * We make sure this function must be executed in some millisecond
>>  */
>> void RT-function()
>> {
>>    some calculation(); <- This doesn't have no dynamic characteristic
>> }
>> int main()
>> {
>>    non-RT-function();
>>    /* This function make sure RT-function cannot preempt by others */
>>    set_RT_max_high_priority();
>>    RT-function A();
>>    set_normal_priority();
>>    non-RT-function();
>> }
>>
>> We don't want realtime in whole function of the task. What we want is
>> just RT-function A.
>> Of course, current Linux cannot make perfectly sure RT-functionA can
>> not preempt by others.
>> That's because some interrupt or exception happen. But RT-function A
>> doesn't related to any dynamic characteristic. What can justify to
>> preempt RT-function A by other processes?
>
> As far as my observation, RT-function always have some syscall. because pure
> calculation doesn't need deterministic guarantee. But _if_ you are really
> using such priority design. I'm ok maximum NonRT priority instead maximum
> RT priority too.

Hmm. It's just example. but it would be not good exmaple.
Let's change it with this.

void RT-function()
{
     int result = some calculation(); <- This doesn't have no dynamic
characteristic
     *mmap_base = result; <-- mmap_base is mapped by GPIO device.
}

Could we allow preemption of this RT function due to other task's
memory pressure?
Of course, Linux is not Hard RT featured OS, I think. So I thinks it
is a policy problem.
If we think system memory pressure is more important than RT task and
we _all_ agree such policy, we can allow it.

But I don't hope it.

-- 
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Minchan Kim

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

[Luis Claudio R. Goncalves]

On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
| > RT Task
| > 
| > void non-RT-function()
| > {
| >    system call();
| >    buffer = malloc();
| >    memset(buffer);
| > }
| > /*
| >  * We make sure this function must be executed in some millisecond
| >  */
| > void RT-function()
| > {
| >    some calculation(); <- This doesn't have no dynamic characteristic
| > }
| > int main()
| > {
| >    non-RT-function();
| >    /* This function make sure RT-function cannot preempt by others */
| >    set_RT_max_high_priority();
| >    RT-function A();
| >    set_normal_priority();
| >    non-RT-function();
| > }
| > 
| > We don't want realtime in whole function of the task. What we want is
| > just RT-function A.
| > Of course, current Linux cannot make perfectly sure RT-functionA can
| > not preempt by others.
| > That's because some interrupt or exception happen. But RT-function A
| > doesn't related to any dynamic characteristic. What can justify to
| > preempt RT-function A by other processes?
| 
| As far as my observation, RT-function always have some syscall. because pure
| calculation doesn't need deterministic guarantee. But _if_ you are really
| using such priority design. I'm ok maximum NonRT priority instead maximum
| RT priority too.

I confess I failed to distinguish memcg OOM and system OOM and used "in
case of OOM kill the selected task the faster you can" as the guideline.
If the exit code path is short that shouldn't be a problem.

Maybe the right way to go would be giving the dying task the biggest
priority inside that memcg to be sure that it will be the next process from
that memcg to be scheduled. Would that be reasonable?

| Luis, NonRT high priority break your use case? and if yes, can you please
| explain the reason?

Most of my tests are in the realtime land, usually with premmpt_rt kernels.
In this case, an RT priority will be usually necessary. But that is not the
general case and I agree that a smoother (but not slower) solution could be
devised by just increasing the dying process'priority to be high enough for
the process set (memcg) it belongs to.

What is the impact of a memcg OOM for the system as a whole? That should be
factored in the equation too.

Luis
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Minchan Kim]

On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> | > RT Task
> | > 
> | > void non-RT-function()
> | > {
> | >    system call();
> | >    buffer = malloc();
> | >    memset(buffer);
> | > }
> | > /*
> | >  * We make sure this function must be executed in some millisecond
> | >  */
> | > void RT-function()
> | > {
> | >    some calculation(); <- This doesn't have no dynamic characteristic
> | > }
> | > int main()
> | > {
> | >    non-RT-function();
> | >    /* This function make sure RT-function cannot preempt by others */
> | >    set_RT_max_high_priority();
> | >    RT-function A();
> | >    set_normal_priority();
> | >    non-RT-function();
> | > }
> | > 
> | > We don't want realtime in whole function of the task. What we want is
> | > just RT-function A.
> | > Of course, current Linux cannot make perfectly sure RT-functionA can
> | > not preempt by others.
> | > That's because some interrupt or exception happen. But RT-function A
> | > doesn't related to any dynamic characteristic. What can justify to
> | > preempt RT-function A by other processes?
> | 
> | As far as my observation, RT-function always have some syscall. because pure
> | calculation doesn't need deterministic guarantee. But _if_ you are really
> | using such priority design. I'm ok maximum NonRT priority instead maximum
> | RT priority too.
> 
> I confess I failed to distinguish memcg OOM and system OOM and used "in
> case of OOM kill the selected task the faster you can" as the guideline.
> If the exit code path is short that shouldn't be a problem.
> 
> Maybe the right way to go would be giving the dying task the biggest
> priority inside that memcg to be sure that it will be the next process from
> that memcg to be scheduled. Would that be reasonable?

Hmm. I can't understand your point. 
What do you mean failing distinguish memcg and system OOM?

We already have been distinguish it by mem_cgroup_out_of_memory.
(but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
So task selected in select_bad_process is one out of memcg's tasks when 
memcg have a memory pressure. 

Isn't it enough?
-- 
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Minchan Kim

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

[Balbir Singh]

* MinChan Kim <minchan.kim@gmail.com> [2010-05-28 23:06:23]:

> > I confess I failed to distinguish memcg OOM and system OOM and used "in
> > case of OOM kill the selected task the faster you can" as the guideline.
> > If the exit code path is short that shouldn't be a problem.
> > 
> > Maybe the right way to go would be giving the dying task the biggest
> > priority inside that memcg to be sure that it will be the next process from
> > that memcg to be scheduled. Would that be reasonable?
> 
> Hmm. I can't understand your point. 
> What do you mean failing distinguish memcg and system OOM?
> 
> We already have been distinguish it by mem_cgroup_out_of_memory.
> (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
> So task selected in select_bad_process is one out of memcg's tasks when 
> memcg have a memory pressure. 
>

We have a routine to help figure out if the task belongs to the memory
cgroup that cause the OOM. The OOM entry from memory cgroup is
different from a regular one. 

-- 
	Three Cheers,
	Balbir

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

[Minchan Kim]

On Fri, May 28, 2010 at 07:50:48PM +0530, Balbir Singh wrote:
> * MinChan Kim <minchan.kim@gmail.com> [2010-05-28 23:06:23]:
> 
> > > I confess I failed to distinguish memcg OOM and system OOM and used "in
> > > case of OOM kill the selected task the faster you can" as the guideline.
> > > If the exit code path is short that shouldn't be a problem.
> > > 
> > > Maybe the right way to go would be giving the dying task the biggest
> > > priority inside that memcg to be sure that it will be the next process from
> > > that memcg to be scheduled. Would that be reasonable?
> > 
> > Hmm. I can't understand your point. 
> > What do you mean failing distinguish memcg and system OOM?
> > 
> > We already have been distinguish it by mem_cgroup_out_of_memory.
> > (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
> > So task selected in select_bad_process is one out of memcg's tasks when 
> > memcg have a memory pressure. 
> >
> 
> We have a routine to help figure out if the task belongs to the memory
> cgroup that cause the OOM. The OOM entry from memory cgroup is
> different from a regular one. 

I meant it. 
My english is poor. "out of" isn't proper. 

> 
> -- 
> 	Three Cheers,
> 	Balbir

-- 
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Minchan Kim

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

[Luis Claudio R. Goncalves]

On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
| On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
| > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
...
| > | As far as my observation, RT-function always have some syscall. because pure
| > | calculation doesn't need deterministic guarantee. But _if_ you are really
| > | using such priority design. I'm ok maximum NonRT priority instead maximum
| > | RT priority too.
| > 
| > I confess I failed to distinguish memcg OOM and system OOM and used "in
| > case of OOM kill the selected task the faster you can" as the guideline.
| > If the exit code path is short that shouldn't be a problem.
| > 
| > Maybe the right way to go would be giving the dying task the biggest
| > priority inside that memcg to be sure that it will be the next process from
| > that memcg to be scheduled. Would that be reasonable?
| 
| Hmm. I can't understand your point. 
| What do you mean failing distinguish memcg and system OOM?
| 
| We already have been distinguish it by mem_cgroup_out_of_memory.
| (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
| So task selected in select_bad_process is one out of memcg's tasks when 
| memcg have a memory pressure. 

The approach of giving the highest priority to the dying task makes sense
in a system wide OOM situation. I though that would also be good for the
memcg OOM case.

After Balbir Singh's comment, I understand that in a memcg OOM the dying
task should have a priority just above the priority of the main task of
that memcg, in order to avoid interfering in the rest of the system.

That is the point where I failed to distinguish between memcg and system OOM.

Should I pursue that new idea of looking for the right priority inside the
memcg or is it overkill? I really don't have a clear view of the impact of
a memcg OOM on system performance - don't know if it is better to solve the
issue sooner (highest RT priority) or leave it to be solved later (highest
prio on the memcg). I have the impression the general case points to the
simpler solution.

Luis
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Minchan Kim]

On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
> On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> ...
> | > | As far as my observation, RT-function always have some syscall. because pure
> | > | calculation doesn't need deterministic guarantee. But _if_ you are really
> | > | using such priority design. I'm ok maximum NonRT priority instead maximum
> | > | RT priority too.
> | > 
> | > I confess I failed to distinguish memcg OOM and system OOM and used "in
> | > case of OOM kill the selected task the faster you can" as the guideline.
> | > If the exit code path is short that shouldn't be a problem.
> | > 
> | > Maybe the right way to go would be giving the dying task the biggest
> | > priority inside that memcg to be sure that it will be the next process from
> | > that memcg to be scheduled. Would that be reasonable?
> | 
> | Hmm. I can't understand your point. 
> | What do you mean failing distinguish memcg and system OOM?
> | 
> | We already have been distinguish it by mem_cgroup_out_of_memory.
> | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
> | So task selected in select_bad_process is one out of memcg's tasks when 
> | memcg have a memory pressure. 
> 
> The approach of giving the highest priority to the dying task makes sense
> in a system wide OOM situation. I though that would also be good for the
> memcg OOM case.
> 
> After Balbir Singh's comment, I understand that in a memcg OOM the dying
> task should have a priority just above the priority of the main task of
> that memcg, in order to avoid interfering in the rest of the system.
> 
> That is the point where I failed to distinguish between memcg and system OOM.
> 
> Should I pursue that new idea of looking for the right priority inside the
> memcg or is it overkill? I really don't have a clear view of the impact of
> a memcg OOM on system performance - don't know if it is better to solve the
> issue sooner (highest RT priority) or leave it to be solved later (highest
> prio on the memcg). I have the impression the general case points to the
> simpler solution.

I think highest RT proirity ins't good solution.
As I mentiond, Some RT functions don't want to be preempted by other processes
which cause memory pressure. It makes RT task broken.

On the other hand, normal processes don't have a requirement of RT.
But it isn't a big problem that it lost little time slice, I think. 
So how about raising max normal priority? 
but I am not sure this is right solution.
Let's listen other's opinion. 
I believe Peter have a good idea.

> 
> Luis
> -- 
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
> 

-- 
Kind regards,
Minchan Kim

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

[Peter Zijlstra]

On Sat, 2010-05-29 at 00:12 +0900, Minchan Kim wrote:
> I think highest RT proirity ins't good solution.
> As I mentiond, Some RT functions don't want to be preempted by other processes
> which cause memory pressure. It makes RT task broken.

All the patches I've seen use MAX_RT_PRIO-1, which is actually FIFO-1,
which is the lowest RT priority.


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

[Minchan Kim]

On Sat, May 29, 2010 at 12:21 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Sat, 2010-05-29 at 00:12 +0900, Minchan Kim wrote:
>> I think highest RT proirity ins't good solution.
>> As I mentiond, Some RT functions don't want to be preempted by other processes
>> which cause memory pressure. It makes RT task broken.
>
> All the patches I've seen use MAX_RT_PRIO-1, which is actually FIFO-1,
> which is the lowest RT priority.

Stupid me. I confused that until now.
That's exactly what I want.


-- 
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Minchan Kim

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

[Luis Claudio R. Goncalves]

On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
| On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
| > On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
| > | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
| > | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
| > ...
| > | > | As far as my observation, RT-function always have some syscall. because pure
| > | > | calculation doesn't need deterministic guarantee. But _if_ you are really
| > | > | using such priority design. I'm ok maximum NonRT priority instead maximum
| > | > | RT priority too.
| > | > 
| > | > I confess I failed to distinguish memcg OOM and system OOM and used "in
| > | > case of OOM kill the selected task the faster you can" as the guideline.
| > | > If the exit code path is short that shouldn't be a problem.
| > | > 
| > | > Maybe the right way to go would be giving the dying task the biggest
| > | > priority inside that memcg to be sure that it will be the next process from
| > | > that memcg to be scheduled. Would that be reasonable?
| > | 
| > | Hmm. I can't understand your point. 
| > | What do you mean failing distinguish memcg and system OOM?
| > | 
| > | We already have been distinguish it by mem_cgroup_out_of_memory.
| > | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
| > | So task selected in select_bad_process is one out of memcg's tasks when 
| > | memcg have a memory pressure. 
| > 
| > The approach of giving the highest priority to the dying task makes sense
| > in a system wide OOM situation. I though that would also be good for the
| > memcg OOM case.
| > 
| > After Balbir Singh's comment, I understand that in a memcg OOM the dying
| > task should have a priority just above the priority of the main task of
| > that memcg, in order to avoid interfering in the rest of the system.
| > 
| > That is the point where I failed to distinguish between memcg and system OOM.
| > 
| > Should I pursue that new idea of looking for the right priority inside the
| > memcg or is it overkill? I really don't have a clear view of the impact of
| > a memcg OOM on system performance - don't know if it is better to solve the
| > issue sooner (highest RT priority) or leave it to be solved later (highest
| > prio on the memcg). I have the impression the general case points to the
| > simpler solution.
| 
| I think highest RT proirity ins't good solution.
| As I mentiond, Some RT functions don't want to be preempted by other processes
| which cause memory pressure. It makes RT task broken.

For the RT case, if you reached a system OOM situation, your determinism has
already been hurt. If the memcg OOM happens on the same memcg your RT task
is - what will probably be the case most of time - again, the determinism
has deteriorated. For both these cases, giving the dying task SCHED_FIFO
MAX_RT_PRIO-1 means a faster recovery.

I don't know what is the system-wide latency effect of a memcg OOM, if any,
or if it would affect an RT task running on another memcg. That is the case
where a more careful priority selection could be necessary.
 
| On the other hand, normal processes don't have a requirement of RT.
| But it isn't a big problem that it lost little time slice, I think. 
| So how about raising max normal priority? 
| but I am not sure this is right solution.
| Let's listen other's opinion. 
| I believe Peter have a good idea.

Thanks again for helping to discuss this idea.

Luis
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Minchan Kim]

On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
> On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
> | > On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
> | > | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> | > | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> | > ...
> | > | > | As far as my observation, RT-function always have some syscall. because pure
> | > | > | calculation doesn't need deterministic guarantee. But _if_ you are really
> | > | > | using such priority design. I'm ok maximum NonRT priority instead maximum
> | > | > | RT priority too.
> | > | > 
> | > | > I confess I failed to distinguish memcg OOM and system OOM and used "in
> | > | > case of OOM kill the selected task the faster you can" as the guideline.
> | > | > If the exit code path is short that shouldn't be a problem.
> | > | > 
> | > | > Maybe the right way to go would be giving the dying task the biggest
> | > | > priority inside that memcg to be sure that it will be the next process from
> | > | > that memcg to be scheduled. Would that be reasonable?
> | > | 
> | > | Hmm. I can't understand your point. 
> | > | What do you mean failing distinguish memcg and system OOM?
> | > | 
> | > | We already have been distinguish it by mem_cgroup_out_of_memory.
> | > | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
> | > | So task selected in select_bad_process is one out of memcg's tasks when 
> | > | memcg have a memory pressure. 
> | > 
> | > The approach of giving the highest priority to the dying task makes sense
> | > in a system wide OOM situation. I though that would also be good for the
> | > memcg OOM case.
> | > 
> | > After Balbir Singh's comment, I understand that in a memcg OOM the dying
> | > task should have a priority just above the priority of the main task of
> | > that memcg, in order to avoid interfering in the rest of the system.
> | > 
> | > That is the point where I failed to distinguish between memcg and system OOM.
> | > 
> | > Should I pursue that new idea of looking for the right priority inside the
> | > memcg or is it overkill? I really don't have a clear view of the impact of
> | > a memcg OOM on system performance - don't know if it is better to solve the
> | > issue sooner (highest RT priority) or leave it to be solved later (highest
> | > prio on the memcg). I have the impression the general case points to the
> | > simpler solution.
> | 
> | I think highest RT proirity ins't good solution.
> | As I mentiond, Some RT functions don't want to be preempted by other processes
> | which cause memory pressure. It makes RT task broken.
> 
> For the RT case, if you reached a system OOM situation, your determinism has
> already been hurt. If the memcg OOM happens on the same memcg your RT task
> is - what will probably be the case most of time - again, the determinism
> has deteriorated. For both these cases, giving the dying task SCHED_FIFO
> MAX_RT_PRIO-1 means a faster recovery.

What I want to say is that determinisic has no relation with OOM. 
Why is some RT task affected by other process's OOM?

Of course, if system has no memory, it is likely to slow down RT task. 
But it's just only thought. If some task scheduled just is exit, we don't need
to raise OOMed task's priority.

But raising min rt priority on your patch was what I want.
It doesn't preempt any RT task.

So until now, I have made noise about your patch.
Really, sorry for that. 
I don't have any objection on raising priority part from now on. 

Thanks, Luis.
-- 
Kind regards,
Minchan Kim

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

[Luis Claudio R. Goncalves]

On Sat, May 29, 2010 at 12:45:49AM +0900, Minchan Kim wrote:
| On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
| > On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
...
| > | I think highest RT proirity ins't good solution.
| > | As I mentiond, Some RT functions don't want to be preempted by other processes
| > | which cause memory pressure. It makes RT task broken.
| > 
| > For the RT case, if you reached a system OOM situation, your determinism has
| > already been hurt. If the memcg OOM happens on the same memcg your RT task
| > is - what will probably be the case most of time - again, the determinism
| > has deteriorated. For both these cases, giving the dying task SCHED_FIFO
| > MAX_RT_PRIO-1 means a faster recovery.
| 
| What I want to say is that determinisic has no relation with OOM. 
| Why is some RT task affected by other process's OOM?
| 
| Of course, if system has no memory, it is likely to slow down RT task. 
| But it's just only thought. If some task scheduled just is exit, we don't need
| to raise OOMed task's priority.
| 
| But raising min rt priority on your patch was what I want.
| It doesn't preempt any RT task.
| 
| So until now, I have made noise about your patch.
| Really, sorry for that. 
| I don't have any objection on raising priority part from now on. 

This is the third version of the patch, factoring in your input along with
Peter's comment. Basically the same patch, but using the lowest RT priority
to boost the dying task.

Thanks again for reviewing and commenting.
Luis

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. Goncalves <lgoncalv@redhat.com>

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)
  */
 static void __oom_kill_task(struct task_struct *p, int verbose)
 {
+	struct sched_param param;
+
 	if (is_global_init(p)) {
 		WARN_ON(1);
 		printk(KERN_WARNING "tried to kill init!\n");
@@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
 	 * exit() and clear out its resources quickly...
 	 */
 	p->time_slice = HZ;
+	param.sched_priority = MAX_RT_PRIO-10;
+	sched_setscheduler(p, SCHED_FIFO, &param);
 	set_tsk_thread_flag(p, TIF_MEMDIE);
 
 	force_sig(SIGKILL, p);
-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[KOSAKI Motohiro]

Hi

> 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. Gonçalves <lgoncalv@redhat.com>

Almostly acceptable to me. but I have two requests, 

- need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
- don't boost priority if it's in mem_cgroup_out_of_memory()

Can you accept this? if not, can you please explain the reason?

Thanks.

> 
> 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)
>   */
>  static void __oom_kill_task(struct task_struct *p, int verbose)
>  {
> +	struct sched_param param;
> +
>  	if (is_global_init(p)) {
>  		WARN_ON(1);
>  		printk(KERN_WARNING "tried to kill init!\n");
> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 * exit() and clear out its resources quickly...
>  	 */
>  	p->time_slice = HZ;
> +	param.sched_priority = MAX_RT_PRIO-10;
> +	sched_setscheduler(p, SCHED_FIFO, &param);
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
>  
>  	force_sig(SIGKILL, p);
> -- 
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
> 



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

[Luis Claudio R. Goncalves]

On Sat, May 29, 2010 at 12:59:09PM +0900, KOSAKI Motohiro wrote:
| Hi
| 
| > 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. Goncalves <lgoncalv@redhat.com>
| 
| Almostly acceptable to me. but I have two requests, 
| 
| - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
| - don't boost priority if it's in mem_cgroup_out_of_memory()
| 
| Can you accept this? if not, can you please explain the reason?
| 
| Thanks.

The last patch I posted was the wrong patch from my queue. Sorry for the
confusion. Here is the last version of the patch, including the suggestions
from Oleg, Peter and Kosaki Motohiro:


oom-kill: give the dying task a higher priority (v4)

In a system under heavy load it was observed that even after the
oom-killer selects a task to die, the task may take a long time to die.

Right before sending a SIGKILL to the task selected by the oom-killer
this task has it's priority increased so that it can exit() exit soon,
freeing memory. That is accomplished by:

        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);

It sounds plausible giving the dying task an even higher priority to be
sure it will be scheduled sooner and free the desired memory. It was
suggested on LKML using SCHED_FIFO:1, the lowest RT priority so that this
task won't interfere with any running RT task.

Another good suggestion, implemented here, was to avoid boosting the dying
task priority in case of mem_cgroup OOM.

Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 709aedf..6a25293 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -380,7 +380,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
  * set.
  */
-static void __oom_kill_task(struct task_struct *p, int verbose)
+static void __oom_kill_task(struct task_struct *p, struct mem_cgroup *mem,
+								int verbose)
 {
 	if (is_global_init(p)) {
 		WARN_ON(1);
@@ -413,11 +414,20 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
 	 */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);
-
 	force_sig(SIGKILL, p);
+	/*
+	 * If this is a system OOM (not a memcg OOM), speed up the recovery
+	 * by boosting the dying task priority to the lowest FIFO priority.
+	 * That helps with the recovery and avoids interfering with RT tasks.
+	 */
+	if (mem == NULL) {
+		struct sched_param param;
+		param.sched_priority = 1;
+		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
+	}
 }
 
-static int oom_kill_task(struct task_struct *p)
+static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
 {
 	/* WARNING: mm may not be dereferenced since we did not obtain its
 	 * value from get_task_mm(p).  This is OK since all we need to do is
@@ -430,7 +440,7 @@ static int oom_kill_task(struct task_struct *p)
 	if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
 		return 1;
 
-	__oom_kill_task(p, 1);
+	__oom_kill_task(p, mem, 1);
 
 	return 0;
 }
@@ -449,7 +459,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 	 * its children or threads, just set TIF_MEMDIE so it can die quickly
 	 */
 	if (p->flags & PF_EXITING) {
-		__oom_kill_task(p, 0);
+		__oom_kill_task(p, mem, 0);
 		return 0;
 	}
 
@@ -462,10 +472,10 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			continue;
 		if (mem && !task_in_mem_cgroup(c, mem))
 			continue;
-		if (!oom_kill_task(c))
+		if (!oom_kill_task(c, mem))
 			return 0;
 	}
-	return oom_kill_task(p);
+	return oom_kill_task(p, mem);
 }
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR

-- 
[ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[Minchan Kim]

Hi, Kosaki.

On Sat, May 29, 2010 at 12:59 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi
>
>> 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. Gonçalves <lgoncalv@redhat.com>
>
> Almostly acceptable to me. but I have two requests,
>
> - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
> - don't boost priority if it's in mem_cgroup_out_of_memory()

Why do you want to not boost priority if it's path of memcontrol?

If it's path of memcontrol and CONFIG_CGROUP_MEM_RES_CTLR is enabled,
mem_cgroup_out_of_memory will select victim task in memcg.
So __oom_kill_task's target task would be in memcg, I think.

As you and memcg guys don't complain this, I would be missing something.
Could you explain it? :)

-- 
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Minchan Kim

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

[KOSAKI Motohiro]

Hi

> Hi, Kosaki.
> 
> On Sat, May 29, 2010 at 12:59 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> > Hi
> >
> >> 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. GonA?alves <lgoncalv@redhat.com>
> >
> > Almostly acceptable to me. but I have two requests,
> >
> > - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
> > - don't boost priority if it's in mem_cgroup_out_of_memory()
> 
> Why do you want to not boost priority if it's path of memcontrol?
> 
> If it's path of memcontrol and CONFIG_CGROUP_MEM_RES_CTLR is enabled,
> mem_cgroup_out_of_memory will select victim task in memcg.
> So __oom_kill_task's target task would be in memcg, I think.

Yep.
But priority boost naturally makes CPU starvation for out of the group
processes.
It seems to break cgroup's isolation concept.

> As you and memcg guys don't complain this, I would be missing something.
> Could you explain it? :)

So, My points are, 

1) Usually priority boost is wrong idea. It have various side effect, but
   system wide OOM is one of exception. In such case, all tasks aren't 
   runnable, then, the downside is acceptable.
2) memcg have OOM notification mechanism. If the admin need priority boost,
   they can do it by their OOM-daemon.

Thanks.


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

[Minchan Kim]

On Mon, May 31, 2010 at 3:35 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi
>
>> Hi, Kosaki.
>>
>> On Sat, May 29, 2010 at 12:59 PM, KOSAKI Motohiro
>> <kosaki.motohiro@jp.fujitsu.com> wrote:
>> > Hi
>> >
>> >> 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. Gonçalves <lgoncalv@redhat.com>
>> >
>> > Almostly acceptable to me. but I have two requests,
>> >
>> > - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
>> > - don't boost priority if it's in mem_cgroup_out_of_memory()
>>
>> Why do you want to not boost priority if it's path of memcontrol?
>>
>> If it's path of memcontrol and CONFIG_CGROUP_MEM_RES_CTLR is enabled,
>> mem_cgroup_out_of_memory will select victim task in memcg.
>> So __oom_kill_task's target task would be in memcg, I think.
>
> Yep.
> But priority boost naturally makes CPU starvation for out of the group
> processes.
> It seems to break cgroup's isolation concept.
>
>> As you and memcg guys don't complain this, I would be missing something.
>> Could you explain it? :)
>
> So, My points are,
>
> 1) Usually priority boost is wrong idea. It have various side effect, but
>   system wide OOM is one of exception. In such case, all tasks aren't
>   runnable, then, the downside is acceptable.
> 2) memcg have OOM notification mechanism. If the admin need priority boost,
>   they can do it by their OOM-daemon.

Is it possible kill the hogging task immediately when the daemon send
kill signal?
I mean we can make OOM daemon higher priority than others and it can
send signal to normal process. but when is normal process exited after
receiving kill signal from OOM daemon? Maybe it's when killed task is
executed by scheduler. It's same problem again, I think.

Kame, Do you have an idea?

> Thanks.
>
>
>



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

[KAMEZAWA Hiroyuki]

On Mon, 31 May 2010 16:05:48 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> On Mon, May 31, 2010 at 3:35 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> > Hi
> >
> >> Hi, Kosaki.
> >>
> >> On Sat, May 29, 2010 at 12:59 PM, KOSAKI Motohiro
> >> <kosaki.motohiro@jp.fujitsu.com> wrote:
> >> > Hi
> >> >
> >> >> 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. GonA?alves <lgoncalv@redhat.com>
> >> >
> >> > Almostly acceptable to me. but I have two requests,
> >> >
> >> > - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
> >> > - don't boost priority if it's in mem_cgroup_out_of_memory()
> >>
> >> Why do you want to not boost priority if it's path of memcontrol?
> >>
> >> If it's path of memcontrol and CONFIG_CGROUP_MEM_RES_CTLR is enabled,
> >> mem_cgroup_out_of_memory will select victim task in memcg.
> >> So __oom_kill_task's target task would be in memcg, I think.
> >
> > Yep.
> > But priority boost naturally makes CPU starvation for out of the group
> > processes.
> > It seems to break cgroup's isolation concept.
> >
> >> As you and memcg guys don't complain this, I would be missing something.
> >> Could you explain it? :)
> >
> > So, My points are,
> >
> > 1) Usually priority boost is wrong idea. It have various side effect, but
> > A  system wide OOM is one of exception. In such case, all tasks aren't
> > A  runnable, then, the downside is acceptable.
> > 2) memcg have OOM notification mechanism. If the admin need priority boost,
> > A  they can do it by their OOM-daemon.
> 
> Is it possible kill the hogging task immediately when the daemon send
> kill signal?
> I mean we can make OOM daemon higher priority than others and it can
> send signal to normal process. but when is normal process exited after
> receiving kill signal from OOM daemon? Maybe it's when killed task is
> executed by scheduler. It's same problem again, I think.
> 
> Kame, Do you have an idea?
> 
This is just an idea and I have no implementaion, yet.

With memcg, oom situation can be recovered by "enlarging limit temporary".
Then, what the daemon has to do is

 1. send signal (kill or other signal to abort for coredump.) 
 2. move a problematic task to a jail if necessary.
 3. enlarge limit for indicating "Go"
 4. After stabilization, reduce the limit.

This is the fastest. Admin has to think of extra-room or jails and
the daemon should be enough clever. But in most case, I think this works well.

Thanks,
-Kame

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

[Minchan Kim]

On Mon, May 31, 2010 at 4:25 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 31 May 2010 16:05:48 +0900
> Minchan Kim <minchan.kim@gmail.com> wrote:
>
>> On Mon, May 31, 2010 at 3:35 PM, KOSAKI Motohiro
>> <kosaki.motohiro@jp.fujitsu.com> wrote:
>> > Hi
>> >
>> >> Hi, Kosaki.
>> >>
>> >> On Sat, May 29, 2010 at 12:59 PM, KOSAKI Motohiro
>> >> <kosaki.motohiro@jp.fujitsu.com> wrote:
>> >> > Hi
>> >> >
>> >> >> 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. Gonçalves <lgoncalv@redhat.com>
>> >> >
>> >> > Almostly acceptable to me. but I have two requests,
>> >> >
>> >> > - need 1) force_sig() 2)sched_setscheduler() order as Oleg mentioned
>> >> > - don't boost priority if it's in mem_cgroup_out_of_memory()
>> >>
>> >> Why do you want to not boost priority if it's path of memcontrol?
>> >>
>> >> If it's path of memcontrol and CONFIG_CGROUP_MEM_RES_CTLR is enabled,
>> >> mem_cgroup_out_of_memory will select victim task in memcg.
>> >> So __oom_kill_task's target task would be in memcg, I think.
>> >
>> > Yep.
>> > But priority boost naturally makes CPU starvation for out of the group
>> > processes.
>> > It seems to break cgroup's isolation concept.
>> >
>> >> As you and memcg guys don't complain this, I would be missing something.
>> >> Could you explain it? :)
>> >
>> > So, My points are,
>> >
>> > 1) Usually priority boost is wrong idea. It have various side effect, but
>> >   system wide OOM is one of exception. In such case, all tasks aren't
>> >   runnable, then, the downside is acceptable.
>> > 2) memcg have OOM notification mechanism. If the admin need priority boost,
>> >   they can do it by their OOM-daemon.
>>
>> Is it possible kill the hogging task immediately when the daemon send
>> kill signal?
>> I mean we can make OOM daemon higher priority than others and it can
>> send signal to normal process. but when is normal process exited after
>> receiving kill signal from OOM daemon? Maybe it's when killed task is
>> executed by scheduler. It's same problem again, I think.
>>
>> Kame, Do you have an idea?
>>
> This is just an idea and I have no implementaion, yet.
>
> With memcg, oom situation can be recovered by "enlarging limit temporary".
> Then, what the daemon has to do is
>
>  1. send signal (kill or other signal to abort for coredump.)
>  2. move a problematic task to a jail if necessary.
>  3. enlarge limit for indicating "Go"
>  4. After stabilization, reduce the limit.
>
> This is the fastest. Admin has to think of extra-room or jails and
> the daemon should be enough clever. But in most case, I think this works well.

I think it is very hard that how much we have to make extra-room since
we can't expect how many tasks are stuck to allocate memory.
But tend to agree that system-wide OOM problem is more important than
memcg's one.
And memcg's guy doesn't seem to have any problem. So I am not against
this patch any more.

Thanks, Kosaki and Kame.

> Thanks,
> -Kame
>
>



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Minchan Kim

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

[Minchan Kim]

On Fri, May 28, 2010 at 01:48:26PM -0300, Luis Claudio R. Goncalves wrote:
> On Sat, May 29, 2010 at 12:45:49AM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
> | > On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
> ...
> | > | I think highest RT proirity ins't good solution.
> | > | As I mentiond, Some RT functions don't want to be preempted by other processes
> | > | which cause memory pressure. It makes RT task broken.
> | > 
> | > For the RT case, if you reached a system OOM situation, your determinism has
> | > already been hurt. If the memcg OOM happens on the same memcg your RT task
> | > is - what will probably be the case most of time - again, the determinism
> | > has deteriorated. For both these cases, giving the dying task SCHED_FIFO
> | > MAX_RT_PRIO-1 means a faster recovery.
> | 
> | What I want to say is that determinisic has no relation with OOM. 
> | Why is some RT task affected by other process's OOM?
> | 
> | Of course, if system has no memory, it is likely to slow down RT task. 
> | But it's just only thought. If some task scheduled just is exit, we don't need
> | to raise OOMed task's priority.
> | 
> | But raising min rt priority on your patch was what I want.
> | It doesn't preempt any RT task.
> | 
> | So until now, I have made noise about your patch.
> | Really, sorry for that. 
> | I don't have any objection on raising priority part from now on. 
> 
> This is the third version of the patch, factoring in your input along with
> Peter's comment. Basically the same patch, but using the lowest RT priority
> to boost the dying task.
> 
> Thanks again for reviewing and commenting.
> Luis
> 
> 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. Goncalves <lgoncalv@redhat.com>
> 
> 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)
>   */
>  static void __oom_kill_task(struct task_struct *p, int verbose)
>  {
> +	struct sched_param param;
> +
>  	if (is_global_init(p)) {
>  		WARN_ON(1);
>  		printk(KERN_WARNING "tried to kill init!\n");
> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 * exit() and clear out its resources quickly...
>  	 */
>  	p->time_slice = HZ;
> +	param.sched_priority = MAX_RT_PRIO-10;

I can't understand your point, still.
Why you put the priority as "MAX_RT_PRIO - 10"?
What I and peter mentioned was "1" which is lowest RT priority. 

> +	sched_setscheduler(p, SCHED_FIFO, &param);

Why do you change sched_setscheduler_nocheck with sched_set_scheduler?
It means you can't boost prioity if current context doesn't have permission.
Is it a your intention?

>  	set_tsk_thread_flag(p, TIF_MEMDIE);
>  
>  	force_sig(SIGKILL, p);
> -- 
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
> 
-- 
Kind regards,
Minchan Kim

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

[KAMEZAWA Hiroyuki]

On Fri, 28 May 2010 13:48:26 -0300
"Luis Claudio R. Goncalves" <lclaudio@uudg.org> wrote:

> On Sat, May 29, 2010 at 12:45:49AM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
> | > On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
> ...
> | > | I think highest RT proirity ins't good solution.
> | > | As I mentiond, Some RT functions don't want to be preempted by other processes
> | > | which cause memory pressure. It makes RT task broken.
> | > 
> | > For the RT case, if you reached a system OOM situation, your determinism has
> | > already been hurt. If the memcg OOM happens on the same memcg your RT task
> | > is - what will probably be the case most of time - again, the determinism
> | > has deteriorated. For both these cases, giving the dying task SCHED_FIFO
> | > MAX_RT_PRIO-1 means a faster recovery.
> | 
> | What I want to say is that determinisic has no relation with OOM. 
> | Why is some RT task affected by other process's OOM?
> | 
> | Of course, if system has no memory, it is likely to slow down RT task. 
> | But it's just only thought. If some task scheduled just is exit, we don't need
> | to raise OOMed task's priority.
> | 
> | But raising min rt priority on your patch was what I want.
> | It doesn't preempt any RT task.
> | 
> | So until now, I have made noise about your patch.
> | Really, sorry for that. 
> | I don't have any objection on raising priority part from now on. 
> 
> This is the third version of the patch, factoring in your input along with
> Peter's comment. Basically the same patch, but using the lowest RT priority
> to boost the dying task.
> 
> Thanks again for reviewing and commenting.
> Luis
> 
> 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. GonA?alves <lgoncalv@redhat.com>
> 
> 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)
>   */
>  static void __oom_kill_task(struct task_struct *p, int verbose)
>  {
> +	struct sched_param param;
> +
>  	if (is_global_init(p)) {
>  		WARN_ON(1);
>  		printk(KERN_WARNING "tried to kill init!\n");
> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 * exit() and clear out its resources quickly...
>  	 */
>  	p->time_slice = HZ;
> +	param.sched_priority = MAX_RT_PRIO-10;
> +	sched_setscheduler(p, SCHED_FIFO, &param);
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
>  

BTW, how about the other threads which share mm_struct ?

Thanks,
-Kame

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

[Minchan Kim]

Hi, Kame.

On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Fri, 28 May 2010 13:48:26 -0300
> "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. Gonçalves <lgoncalv@redhat.com>
>>
>> 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)
>>   */
>>  static void __oom_kill_task(struct task_struct *p, int verbose)
>>  {
>> +     struct sched_param param;
>> +
>>       if (is_global_init(p)) {
>>               WARN_ON(1);
>>               printk(KERN_WARNING "tried to kill init!\n");
>> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>>        * exit() and clear out its resources quickly...
>>        */
>>       p->time_slice = HZ;
>> +     param.sched_priority = MAX_RT_PRIO-10;
>> +     sched_setscheduler(p, SCHED_FIFO, &param);
>>       set_tsk_thread_flag(p, TIF_MEMDIE);
>>
>
> BTW, how about the other threads which share mm_struct ?

Could you elaborate your intention? :)

>
> Thanks,
> -Kame
>
>



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

[KAMEZAWA Hiroyuki]

On Mon, 31 May 2010 14:01:03 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> Hi, Kame.
> 
> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > On Fri, 28 May 2010 13:48:26 -0300
> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. GonA?alves <lgoncalv@redhat.com>
> >>
> >> 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)
> >> A  */
> >> A static void __oom_kill_task(struct task_struct *p, int verbose)
> >> A {
> >> + A  A  struct sched_param param;
> >> +
> >> A  A  A  if (is_global_init(p)) {
> >> A  A  A  A  A  A  A  WARN_ON(1);
> >> A  A  A  A  A  A  A  printk(KERN_WARNING "tried to kill init!\n");
> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >> A  A  A  A * exit() and clear out its resources quickly...
> >> A  A  A  A */
> >> A  A  A  p->time_slice = HZ;
> >> + A  A  param.sched_priority = MAX_RT_PRIO-10;
> >> + A  A  sched_setscheduler(p, SCHED_FIFO, &param);
> >> A  A  A  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.

Thanks,
-Kame



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

[Minchan Kim]

On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 31 May 2010 14:01:03 +0900
> Minchan Kim <minchan.kim@gmail.com> wrote:
>
>> Hi, Kame.
>>
>> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Fri, 28 May 2010 13:48:26 -0300
>> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. Gonçalves <lgoncalv@redhat.com>
>> >>
>> >> 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)
>> >>   */
>> >>  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >>  {
>> >> +     struct sched_param param;
>> >> +
>> >>       if (is_global_init(p)) {
>> >>               WARN_ON(1);
>> >>               printk(KERN_WARNING "tried to kill init!\n");
>> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >>        * exit() and clear out its resources quickly...
>> >>        */
>> >>       p->time_slice = HZ;
>> >> +     param.sched_priority = MAX_RT_PRIO-10;
>> >> +     sched_setscheduler(p, SCHED_FIFO, &param);
>> >>       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  KILL signal, the process include
the thread will be killed.

I think
> Thanks,
> -Kame
>
>
>
>



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Minchan Kim

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

[KAMEZAWA Hiroyuki]

On Mon, 31 May 2010 14:46:05 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > On Mon, 31 May 2010 14:01:03 +0900
> > Minchan Kim <minchan.kim@gmail.com> wrote:
> >
> >> Hi, Kame.
> >>
> >> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >> > On Fri, 28 May 2010 13:48:26 -0300
> >> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. GonA?alves <lgoncalv@redhat.com>
> >> >>
> >> >> 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)
> >> >> A  */
> >> >> A static void __oom_kill_task(struct task_struct *p, int verbose)
> >> >> A {
> >> >> + A  A  struct sched_param param;
> >> >> +
> >> >> A  A  A  if (is_global_init(p)) {
> >> >> A  A  A  A  A  A  A  WARN_ON(1);
> >> >> A  A  A  A  A  A  A  printk(KERN_WARNING "tried to kill init!\n");
> >> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >> >> A  A  A  A * exit() and clear out its resources quickly...
> >> >> A  A  A  A */
> >> >> A  A  A  p->time_slice = HZ;
> >> >> + A  A  param.sched_priority = MAX_RT_PRIO-10;
> >> >> + A  A  sched_setscheduler(p, SCHED_FIFO, &param);
> >> >> A  A  A  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  KILL 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.

Thanks,
-Kame

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

[Minchan Kim]

On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 31 May 2010 14:46:05 +0900
> Minchan Kim <minchan.kim@gmail.com> wrote:
>
>> On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Mon, 31 May 2010 14:01:03 +0900
>> > Minchan Kim <minchan.kim@gmail.com> wrote:
>> >
>> >> Hi, Kame.
>> >>
>> >> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
>> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> >> > On Fri, 28 May 2010 13:48:26 -0300
>> >> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. Gonçalves <lgoncalv@redhat.com>
>> >> >>
>> >> >> 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)
>> >> >>   */
>> >> >>  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >>  {
>> >> >> +     struct sched_param param;
>> >> >> +
>> >> >>       if (is_global_init(p)) {
>> >> >>               WARN_ON(1);
>> >> >>               printk(KERN_WARNING "tried to kill init!\n");
>> >> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >>        * exit() and clear out its resources quickly...
>> >> >>        */
>> >> >>       p->time_slice = HZ;
>> >> >> +     param.sched_priority = MAX_RT_PRIO-10;
>> >> >> +     sched_setscheduler(p, SCHED_FIFO, &param);
>> >> >>       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  KILL 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?

>
> Thanks,
> -Kame
>
>



-- 
Kind regards,
Minchan Kim

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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@gmail.com> wrote:

> On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > On Mon, 31 May 2010 14:46:05 +0900
> > Minchan Kim <minchan.kim@gmail.com> wrote:
> >
> >> On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >> > On Mon, 31 May 2010 14:01:03 +0900
> >> > Minchan Kim <minchan.kim@gmail.com> wrote:
> >> >
> >> >> Hi, Kame.
> >> >>
> >> >> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
> >> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >> >> > On Fri, 28 May 2010 13:48:26 -0300
> >> >> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. GonA?alves <lgoncalv@redhat.com>
> >> >> >>
> >> >> >> 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)
> >> >> >> A  */
> >> >> >> A static void __oom_kill_task(struct task_struct *p, int verbose)
> >> >> >> A {
> >> >> >> + A  A  struct sched_param param;
> >> >> >> +
> >> >> >> A  A  A  if (is_global_init(p)) {
> >> >> >> A  A  A  A  A  A  A  WARN_ON(1);
> >> >> >> A  A  A  A  A  A  A  printk(KERN_WARNING "tried to kill init!\n");
> >> >> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >> >> >> A  A  A  A * exit() and clear out its resources quickly...
> >> >> >> A  A  A  A */
> >> >> >> A  A  A  p->time_slice = HZ;
> >> >> >> + A  A  param.sched_priority = MAX_RT_PRIO-10;
> >> >> >> + A  A  sched_setscheduler(p, SCHED_FIFO, &param);
> >> >> >> A  A  A  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 A KILL 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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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@jp.fujitsu.com> wrote:
> On Mon, 31 May 2010 15:09:41 +0900
> Minchan Kim <minchan.kim@gmail.com> wrote:
>
>> On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Mon, 31 May 2010 14:46:05 +0900
>> > Minchan Kim <minchan.kim@gmail.com> wrote:
>> >
>> >> On Mon, May 31, 2010 at 2:04 PM, KAMEZAWA Hiroyuki
>> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> >> > On Mon, 31 May 2010 14:01:03 +0900
>> >> > Minchan Kim <minchan.kim@gmail.com> wrote:
>> >> >
>> >> >> Hi, Kame.
>> >> >>
>> >> >> On Mon, May 31, 2010 at 9:21 AM, KAMEZAWA Hiroyuki
>> >> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> >> >> > On Fri, 28 May 2010 13:48:26 -0300
>> >> >> > "Luis Claudio R. Goncalves" <lclaudio@uudg.org> 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. Gonçalves <lgoncalv@redhat.com>
>> >> >> >>
>> >> >> >> 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)
>> >> >> >>   */
>> >> >> >>  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >> >>  {
>> >> >> >> +     struct sched_param param;
>> >> >> >> +
>> >> >> >>       if (is_global_init(p)) {
>> >> >> >>               WARN_ON(1);
>> >> >> >>               printk(KERN_WARNING "tried to kill init!\n");
>> >> >> >> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >> >> >>        * exit() and clear out its resources quickly...
>> >> >> >>        */
>> >> >> >>       p->time_slice = HZ;
>> >> >> >> +     param.sched_priority = MAX_RT_PRIO-10;
>> >> >> >> +     sched_setscheduler(p, SCHED_FIFO, &param);
>> >> >> >>       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  KILL 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.

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

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

>
> Thanks,
> -Kame
>
>



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

[Luis Claudio R. Goncalves]

On Mon, May 31, 2010 at 03:51:02PM +0900, KAMEZAWA Hiroyuki wrote:
| On Mon, 31 May 2010 15:09:41 +0900
| Minchan Kim <minchan.kim@gmail.com> wrote:
| > On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
| > <kamezawa.hiroyu@jp.fujitsu.com> wrote:
...
| > >> > 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  KILL 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.

This is a good point...

| 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.

I understand (from the comments in the code) the badness calculation gives more
points to the siblings in a thread that have their own mm. I wonder if what you
are describing is not a corner case.

Again, your idea sounds like an interesting refinement to the patch. I am
just not sure this change should implemented now or in a second round of
changes.

| 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.

If my understanding of badness() is right, I wouldn't be ashamed of saying
that it seems to be _a bit_ overkill. But I may be wrong in my
interpretation.

While re-reading the code I noticed that in select_bad_process() we can
eventually bump on an already dying task, case in which we just wait for
the task to die and avoid killing other tasks. Maybe we could boost the
priority of the dying task here too.

Luis
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[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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

[KAMEZAWA Hiroyuki]

On Mon, 31 May 2010 10:52:27 -0300
"Luis Claudio R. Goncalves" <lclaudio@uudg.org> wrote:

> | 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.
> 
> If my understanding of badness() is right, I wouldn't be ashamed of saying
> that it seems to be _a bit_ overkill. But I may be wrong in my
> interpretation.
> 
> While re-reading the code I noticed that in select_bad_process() we can
> eventually bump on an already dying task, case in which we just wait for
> the task to die and avoid killing other tasks. Maybe we could boost the
> priority of the dying task here too.
> 
yes, nice catch.

Thanks,
-Kame

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

[Luis Claudio R. Goncalves]

On Tue, Jun 01, 2010 at 08:50:06AM +0900, KAMEZAWA Hiroyuki wrote:
| On Mon, 31 May 2010 10:52:27 -0300
| "Luis Claudio R. Goncalves" <lclaudio@uudg.org> wrote:
| 
| > | 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.
| > 
| > If my understanding of badness() is right, I wouldn't be ashamed of saying
| > that it seems to be _a bit_ overkill. But I may be wrong in my
| > interpretation.
| > 
| > While re-reading the code I noticed that in select_bad_process() we can
| > eventually bump on an already dying task, case in which we just wait for
| > the task to die and avoid killing other tasks. Maybe we could boost the
| > priority of the dying task here too.
| > 
| yes, nice catch.

Here is a more complete version of the patch, boosting priority on the
three exit points of the OOM-killer. I also avoid touching the priority if
the task is already an RT task. The patch:

 
oom-kill: give the dying task a higher priority (v5)

In a system under heavy load it was observed that even after the
oom-killer selects a task to die, the task may take a long time to die.

Right before sending a SIGKILL to the task selected by the oom-killer
this task has it's priority increased so that it can exit() exit soon,
freeing memory. That is accomplished by:

        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);

It sounds plausible giving the dying task an even higher priority to be
sure it will be scheduled sooner and free the desired memory. It was
suggested on LKML using SCHED_FIFO:1, the lowest RT priority so that
this task won't interfere with any running RT task.

If the dying task is already an RT task, leave it untouched.

Another good suggestion, implemented here, was to avoid boosting the
dying task priority in case of mem_cgroup OOM.

Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 709aedf..67e18ca 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -52,6 +52,22 @@ static int has_intersects_mems_allowed(struct task_struct *tsk)
 	return 0;
 }
 
+/*
+ * If this is a system OOM (not a memcg OOM) and the task selected to be
+ * killed is not already running at high (RT) priorities, speed up the
+ * recovery by boosting the dying task to the lowest FIFO priority.
+ * That helps with the recovery and avoids interfering with RT tasks.
+ */
+static void boost_dying_task_prio(struct task_struct *p,
+					struct mem_cgroup *mem)
+{
+	if ((mem == NULL) && !rt_task(p)) {
+		struct sched_param param;
+		param.sched_priority = 1;
+		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
+	}
+}
+
 /**
  * badness - calculate a numeric value for how bad this task has been
  * @p: task struct of which task we should calculate
@@ -277,8 +293,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 		 * blocked waiting for another task which itself is waiting
 		 * for memory. Is there a better alternative?
 		 */
-		if (test_tsk_thread_flag(p, TIF_MEMDIE))
+		if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
+			boost_dying_task_prio(p, mem);
 			return ERR_PTR(-1UL);
+		}
 
 		/*
 		 * This is in the process of releasing memory so wait for it
@@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 		 * Otherwise we could get an easy OOM deadlock.
 		 */
 		if (p->flags & PF_EXITING) {
-			if (p != current)
+			if (p != current) {
+				boost_dying_task_prio(p, mem);
 				return ERR_PTR(-1UL);
-
+			}
 			chosen = p;
 			*ppoints = ULONG_MAX;
 		}
@@ -380,7 +399,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
  * set.
  */
-static void __oom_kill_task(struct task_struct *p, int verbose)
+static void __oom_kill_task(struct task_struct *p, struct mem_cgroup *mem,
+								int verbose)
 {
 	if (is_global_init(p)) {
 		WARN_ON(1);
@@ -413,11 +433,11 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
 	 */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);
-
 	force_sig(SIGKILL, p);
+	boost_dying_task_prio(p, mem);
 }
 
-static int oom_kill_task(struct task_struct *p)
+static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
 {
 	/* WARNING: mm may not be dereferenced since we did not obtain its
 	 * value from get_task_mm(p).  This is OK since all we need to do is
@@ -430,7 +450,7 @@ static int oom_kill_task(struct task_struct *p)
 	if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
 		return 1;
 
-	__oom_kill_task(p, 1);
+	__oom_kill_task(p, mem, 1);
 
 	return 0;
 }
@@ -449,7 +469,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 	 * its children or threads, just set TIF_MEMDIE so it can die quickly
 	 */
 	if (p->flags & PF_EXITING) {
-		__oom_kill_task(p, 0);
+		__oom_kill_task(p, mem, 0);
 		return 0;
 	}
 
@@ -462,10 +482,10 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			continue;
 		if (mem && !task_in_mem_cgroup(c, mem))
 			continue;
-		if (!oom_kill_task(c))
+		if (!oom_kill_task(c, mem))
 			return 0;
 	}
-	return oom_kill_task(p);
+	return oom_kill_task(p, mem);
 }
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR

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

[David Rientjes]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 3350 bytes --]

On Tue, 1 Jun 2010, Luis Claudio R. Goncalves wrote:

> oom-kill: give the dying task a higher priority (v5)
> 
> In a system under heavy load it was observed that even after the
> oom-killer selects a task to die, the task may take a long time to die.
> 
> Right before sending a SIGKILL to the task selected by the oom-killer
> this task has it's priority increased so that it can exit() exit soon,
> freeing memory. That is accomplished by:
> 
>         /*
>          * We give our sacrificial lamb high priority and access to
>          * all the memory it needs. That way it should be able to
>          * exit() and clear out its resources quickly...
>          */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> 
> It sounds plausible giving the dying task an even higher priority to be
> sure it will be scheduled sooner and free the desired memory. It was
> suggested on LKML using SCHED_FIFO:1, the lowest RT priority so that
> this task won't interfere with any running RT task.
> 
> If the dying task is already an RT task, leave it untouched.
> 
> Another good suggestion, implemented here, was to avoid boosting the
> dying task priority in case of mem_cgroup OOM.
> 
> Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 709aedf..67e18ca 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -52,6 +52,22 @@ static int has_intersects_mems_allowed(struct task_struct *tsk)
>  	return 0;
>  }
>  
> +/*
> + * If this is a system OOM (not a memcg OOM) and the task selected to be
> + * killed is not already running at high (RT) priorities, speed up the
> + * recovery by boosting the dying task to the lowest FIFO priority.
> + * That helps with the recovery and avoids interfering with RT tasks.
> + */
> +static void boost_dying_task_prio(struct task_struct *p,
> +					struct mem_cgroup *mem)
> +{
> +	if ((mem == NULL) && !rt_task(p)) {
> +		struct sched_param param;
> +		param.sched_priority = 1;
> +		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> +	}
> +}
> +
>  /**
>   * badness - calculate a numeric value for how bad this task has been
>   * @p: task struct of which task we should calculate
> @@ -277,8 +293,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>  		 * blocked waiting for another task which itself is waiting
>  		 * for memory. Is there a better alternative?
>  		 */
> -		if (test_tsk_thread_flag(p, TIF_MEMDIE))
> +		if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
> +			boost_dying_task_prio(p, mem);
>  			return ERR_PTR(-1UL);
> +		}
>  
>  		/*
>  		 * This is in the process of releasing memory so wait for it

That's unnecessary, if p already has TIF_MEMDIE set, then 
boost_dying_task_prio(p) has already been called.

> @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>  		 * Otherwise we could get an easy OOM deadlock.
>  		 */
>  		if (p->flags & PF_EXITING) {
> -			if (p != current)
> +			if (p != current) {
> +				boost_dying_task_prio(p, mem);
>  				return ERR_PTR(-1UL);
> -
> +			}
>  			chosen = p;
>  			*ppoints = ULONG_MAX;
>  		}

This has the potential to actually make it harder to free memory if p is 
waiting to acquire a writelock on mm->mmap_sem in the exit path while the 
thread holding mm->mmap_sem is trying to run.

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

[KOSAKI Motohiro]

> > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> >  		 * Otherwise we could get an easy OOM deadlock.
> >  		 */
> >  		if (p->flags & PF_EXITING) {
> > -			if (p != current)
> > +			if (p != current) {
> > +				boost_dying_task_prio(p, mem);
> >  				return ERR_PTR(-1UL);
> > -
> > +			}
> >  			chosen = p;
> >  			*ppoints = ULONG_MAX;
> >  		}
> 
> This has the potential to actually make it harder to free memory if p is 
> waiting to acquire a writelock on mm->mmap_sem in the exit path while the 
> thread holding mm->mmap_sem is trying to run.

if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.


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

[Luis Claudio R. Goncalves]

On Wed, Jun 02, 2010 at 10:54:01PM +0900, KOSAKI Motohiro wrote:
| > > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
| > >  		 * Otherwise we could get an easy OOM deadlock.
| > >  		 */
| > >  		if (p->flags & PF_EXITING) {
| > > -			if (p != current)
| > > +			if (p != current) {
| > > +				boost_dying_task_prio(p, mem);
| > >  				return ERR_PTR(-1UL);
| > > -
| > > +			}
| > >  			chosen = p;
| > >  			*ppoints = ULONG_MAX;
| > >  		}
| > 
| > This has the potential to actually make it harder to free memory if p is 
| > waiting to acquire a writelock on mm->mmap_sem in the exit path while the 
| > thread holding mm->mmap_sem is trying to run.
| 
| if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.

Ok, that was not a good idea after all :)

But I understand the !rt_task(p) test is necessary to avoid decrementing
the priority of an eventual RT task selected to die. Though it may also be
a corner case in badness().

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

[David Rientjes]

On Wed, 2 Jun 2010, KOSAKI Motohiro wrote:

> > > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> > >  		 * Otherwise we could get an easy OOM deadlock.
> > >  		 */
> > >  		if (p->flags & PF_EXITING) {
> > > -			if (p != current)
> > > +			if (p != current) {
> > > +				boost_dying_task_prio(p, mem);
> > >  				return ERR_PTR(-1UL);
> > > -
> > > +			}
> > >  			chosen = p;
> > >  			*ppoints = ULONG_MAX;
> > >  		}
> > 
> > This has the potential to actually make it harder to free memory if p is 
> > waiting to acquire a writelock on mm->mmap_sem in the exit path while the 
> > thread holding mm->mmap_sem is trying to run.
> 
> if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.
> 

And that can reduce the runtime of the thread holding a writelock on 
mm->mmap_sem, making the exit actually take longer than without the patch 
if its priority is significantly higher, especially on smaller machines.

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

[KOSAKI Motohiro]

> On Wed, 2 Jun 2010, KOSAKI Motohiro wrote:
> 
> > > > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> > > >  		 * Otherwise we could get an easy OOM deadlock.
> > > >  		 */
> > > >  		if (p->flags & PF_EXITING) {
> > > > -			if (p != current)
> > > > +			if (p != current) {
> > > > +				boost_dying_task_prio(p, mem);
> > > >  				return ERR_PTR(-1UL);
> > > > -
> > > > +			}
> > > >  			chosen = p;
> > > >  			*ppoints = ULONG_MAX;
> > > >  		}
> > > 
> > > This has the potential to actually make it harder to free memory if p is 
> > > waiting to acquire a writelock on mm->mmap_sem in the exit path while the 
> > > thread holding mm->mmap_sem is trying to run.
> > 
> > if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.
> > 
> 
> And that can reduce the runtime of the thread holding a writelock on 
> mm->mmap_sem, making the exit actually take longer than without the patch 
> if its priority is significantly higher, especially on smaller machines.

If p need mmap_sem, p is going to sleep to wait mmap_sem. if p doesn't,
quickly exit is good thing. In other word, task fairness is not our goal
when oom occur.



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

[Minchan Kim]

On Thu, Jun 3, 2010 at 8:36 AM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> On Wed, 2 Jun 2010, KOSAKI Motohiro wrote:
>>
>> > > > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>> > > >                  * Otherwise we could get an easy OOM deadlock.
>> > > >                  */
>> > > >                 if (p->flags & PF_EXITING) {
>> > > > -                       if (p != current)
>> > > > +                       if (p != current) {
>> > > > +                               boost_dying_task_prio(p, mem);
>> > > >                                 return ERR_PTR(-1UL);
>> > > > -
>> > > > +                       }
>> > > >                         chosen = p;
>> > > >                         *ppoints = ULONG_MAX;
>> > > >                 }
>> > >
>> > > This has the potential to actually make it harder to free memory if p is
>> > > waiting to acquire a writelock on mm->mmap_sem in the exit path while the
>> > > thread holding mm->mmap_sem is trying to run.
>> >
>> > if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.
>> >
>>
>> And that can reduce the runtime of the thread holding a writelock on
>> mm->mmap_sem, making the exit actually take longer than without the patch
>> if its priority is significantly higher, especially on smaller machines.
>
> If p need mmap_sem, p is going to sleep to wait mmap_sem. if p doesn't,
> quickly exit is good thing. In other word, task fairness is not our goal
> when oom occur.
>

Tend to agree. I didn't agree boosting of whole threads' priority.

Task fairness VS system hang is trade off. task fairness is best
effort but system hang is critical.
Also, we have tried to it.

        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
        p->rt.time_slice = HZ;
        set_tsk_thread_flag(p, TIF_MEMDIE);

But I think above code is meaningless unless p use SCHED_RR.
So boosting of lowest RT priority with FIFO is to meet above comment's
goal, I think.

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

[Peter Zijlstra]

On Wed, 2010-06-02 at 14:11 -0700, David Rientjes wrote:
> 
> And that can reduce the runtime of the thread holding a writelock on 
> mm->mmap_sem, making the exit actually take longer than without the patch 
> if its priority is significantly higher, especially on smaller machines. 

/me smells an inversion... on -rt we solved those ;-)

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

[David Rientjes]

On Thu, 3 Jun 2010, Peter Zijlstra wrote:

> > And that can reduce the runtime of the thread holding a writelock on 
> > mm->mmap_sem, making the exit actually take longer than without the patch 
> > if its priority is significantly higher, especially on smaller machines. 
> 
> /me smells an inversion... on -rt we solved those ;-)
> 

Right, but I don't see how increasing an oom killed tasks priority to a 
divine priority doesn't impact the priorities of other tasks which may be 
blocking the exit of that task, namely a coredumper or holder of 
mm->mmap_sem.  This patch also doesn't address how it negatively impacts 
the priorities of jobs running in different cpusets (although sharing the 
same cpus) because one cpuset is oom.

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

[Minchan Kim]

On Mon, May 31, 2010 at 10:52 PM, Luis Claudio R. Goncalves
<lclaudio@uudg.org> wrote:
> On Mon, May 31, 2010 at 03:51:02PM +0900, KAMEZAWA Hiroyuki wrote:
> | On Mon, 31 May 2010 15:09:41 +0900
> | Minchan Kim <minchan.kim@gmail.com> wrote:
> | > On Mon, May 31, 2010 at 2:54 PM, KAMEZAWA Hiroyuki
> | > <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> ...
> | > >> > 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  KILL 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.
>
> This is a good point...
>
> | 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.
>
> I understand (from the comments in the code) the badness calculation gives more
> points to the siblings in a thread that have their own mm. I wonder if what you
> are describing is not a corner case.
>
> Again, your idea sounds like an interesting refinement to the patch. I am
> just not sure this change should implemented now or in a second round of
> changes.

First of all, I think your patch is first.
That's because I am not sure this logic is effective.


        /*
         * We give our sacrificial lamb high priority and access to
         * all the memory it needs. That way it should be able to
         * exit() and clear out its resources quickly...
         */
        p->rt.time_slice = HZ;

Peter changed it in fa717060f1ab.
Now if we change rt.time_slice as HZ, it means the task have high priority?
I am not a scheduler expert. but as I looked through scheduler code,
rt.time_slice is only related to RT scheduler. so if we uses CFS, it
doesn't make task high priority.
Perter, Right?

If it is right, I think Luis patch will fix it.

Secondly, as Kame pointed out, we have to raise whole thread's
priority to kill victim process for reclaiming pages. But I think it
has deadlock problem.
If we raise whole threads's priority and some thread has dependency of
other thread which is blocked, it makes system deadlock. So I think
it's not easy part.

If this part is really big problem, we should consider it more carefully.

>
> | 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.
>
> If my understanding of badness() is right, I wouldn't be ashamed of saying
> that it seems to be _a bit_ overkill. But I may be wrong in my
> interpretation.
>
> While re-reading the code I noticed that in select_bad_process() we can
> eventually bump on an already dying task, case in which we just wait for
> the task to die and avoid killing other tasks. Maybe we could boost the
> priority of the dying task here too.

Yes. It is good where we boost priority of task, I think.

>
> Luis
> --
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
>
>



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

[David Rientjes]

On Tue, 1 Jun 2010, Minchan Kim wrote:

> Secondly, as Kame pointed out, we have to raise whole thread's
> priority to kill victim process for reclaiming pages. But I think it
> has deadlock problem.

Agreed, this has the potential to actually increase the amount of time for 
an oom killed task to fully exit: the exit path takes mm->mmap_sem on exit 
and if that is held by another thread waiting for the oom killed task to 
exit (i.e. reclaim has failed and the oom killer becomes a no-op because 
it sees an already killed task) then there's a livelock.  That's always 
been a problem, but is compounded with increasing the priority of a task 
not holding mm->mmap_sem if the thread holding the writelock actually 
isn't looking for memory but simply doesn't get a chance to release 
because it fails to run.

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

[Balbir Singh]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2010-05-28 13:46:53]:

> > * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
> > 
> > > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> > >   */
> > >  static void __oom_kill_task(struct task_struct *p, int verbose)
> > >  {
> > > +	struct sched_param param;
> > > +
> > >  	if (is_global_init(p)) {
> > >  		WARN_ON(1);
> > >  		printk(KERN_WARNING "tried to kill init!\n");
> > > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> > >  	 */
> > >  	p->rt.time_slice = HZ;
> > >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > > -
> > >  	force_sig(SIGKILL, p);
> > > +	param.sched_priority = MAX_RT_PRIO-1;
> > > +	sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> > >  }
> > >
> > 
> > I would like to understand the visible benefits of this patch. Have
> > you seen an OOM kill tasked really get bogged down. Should this task
> > really be competing with other important tasks for run time?
> 
> What you mean important? Until OOM victim task exit completely, the system have no memory.
> all of important task can't do anything.
> 
> In almost kernel subsystems, automatically priority boost is really bad idea because
> it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
> was alread broken by memory starvation.
>

I am still not convinced, specially if we are running under mem
cgroup. Even setting SCHED_FIFO does not help, you could have other
things like cpusets that might restrict the CPUs you can run on, or
any other policy and we could end up contending anyway with other
SCHED_FIFO tasks.
 
> That's the reason I acked it.

If we could show faster recovery from OOM or anything else, I would be
more convinced.

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	Three Cheers,
	Balbir

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

[KAMEZAWA Hiroyuki]

On Fri, 28 May 2010 11:57:01 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> I am still not convinced, specially if we are running under mem
> cgroup. Even setting SCHED_FIFO does not help, you could have other
> things like cpusets that might restrict the CPUs you can run on, or
> any other policy and we could end up contending anyway with other
> SCHED_FIFO tasks.
>  
> > That's the reason I acked it.
> 
> If we could show faster recovery from OOM or anything else, I would be
> more convinced.
> 
Off topic.

 1. Run a daemon in the highest RT priority.
 2. disable OOM for a mem cgroup.
 3. The daemon register oom-event-notifier of the mem cgroup.

 When OOM happens.
 4. The daemon receive a event, and then,
    a) enlarge limit
    or
    b) kill a task 
    or
    c) enlarge limit temporary and kill a task, later, reduce limit again.

This is the fastest and promissing operation for memcg users.

memcg's oom slowdown happens just because it's limited by a user configuration
not by the system. That's a point to be considered.
The oom situation can be _immediaterly_ fixed up by enlarge limit as emergency mode.

If you has to wait for the end of a task, there will be delay, it's unavoidable.

Thanks,
-Kame



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

[KOSAKI Motohiro]

> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2010-05-28 13:46:53]:
> 
> > > * Luis Claudio R. Goncalves <lclaudio@uudg.org> [2010-05-28 00:51:47]:
> > > 
> > > > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> > > >   */
> > > >  static void __oom_kill_task(struct task_struct *p, int verbose)
> > > >  {
> > > > +	struct sched_param param;
> > > > +
> > > >  	if (is_global_init(p)) {
> > > >  		WARN_ON(1);
> > > >  		printk(KERN_WARNING "tried to kill init!\n");
> > > > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> > > >  	 */
> > > >  	p->rt.time_slice = HZ;
> > > >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > > > -
> > > >  	force_sig(SIGKILL, p);
> > > > +	param.sched_priority = MAX_RT_PRIO-1;
> > > > +	sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> > > >  }
> > > >
> > > 
> > > I would like to understand the visible benefits of this patch. Have
> > > you seen an OOM kill tasked really get bogged down. Should this task
> > > really be competing with other important tasks for run time?
> > 
> > What you mean important? Until OOM victim task exit completely, the system have no memory.
> > all of important task can't do anything.
> > 
> > In almost kernel subsystems, automatically priority boost is really bad idea because
> > it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
> > was alread broken by memory starvation.
> >
> 
> I am still not convinced, specially if we are running under mem
> cgroup. Even setting SCHED_FIFO does not help, you could have other
> things like cpusets that might restrict the CPUs you can run on, or
> any other policy and we could end up contending anyway with other
> SCHED_FIFO tasks.

Ah, right you are. I had missed mem-cgroup.
But I think memcgroup also don't need following two boost. Can we get rid of it?

	p->rt.time_slice = HZ;
	set_tsk_thread_flag(p, TIF_MEMDIE);


I mean we need distinguish global oom and memcg oom, perhapls. 


> > That's the reason I acked it.
> 
> If we could show faster recovery from OOM or anything else, I would be
> more convinced.






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

[Peter Zijlstra]

On Fri, 2010-05-28 at 00:51 -0300, Luis Claudio R. Goncalves wrote:
> +       param.sched_priority = MAX_RT_PRIO-1;
> +       sched_setscheduler_nocheck(p, SCHED_FIFO, &param);


Argh, so you got me confused as well.

the sched_param ones are userspace values, so you should be using 1.


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