On Thu, 10 Jun 2010 03:21:01 +0200
Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 06/10, KAMEZAWA Hiroyuki wrote:
> >
> > On Wed, 9 Jun 2010 22:14:30 +0200
> > Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > > > in this case since it would
> > > > not be allocating memory without p->mm.
> > >
> > > This thread will not allocate the memory, yes. But its sub-threads can.
> > > And select_bad_process() can constantly return the same (dead) thread P,
> > > badness() inspects ->mm under find_lock_task_mm() which finds the thread
> > > with the valid ->mm.
> > >
> > > OK. Probably this doesn't matter. I don't know if task_in_mem_cgroup(task)
> > > was fixed or not, but currently it also looks at task->mm and thus have
> > > the same boring problem: it is trivial to make the memory-hog process
> > > invisible to oom. Unless I missed something, of course.
> >
> > HmHm...your concern is that there is a case when mem_cgroup_out_of_memory()
> > can't kill anything ?
>
> Or it can kill the wrong task. But once again, I am only speculating
> looking at the current code.
>
> > Now, memcg doesn't return -ENOMEM in usual case.
> > So, it loops until there are some available memory under its limit.
> > Then, if memory_cgroup_out_of_memory() can kill a process in several trial,
> > we'll not have terrible problem. (even if it's slow.)
> >
> > Hmm. What I can't understand is whether there is a case when PF_EXITING
> > thread never exit. If so, we need some care (in memcg?)
>
> void *thread_func(void *)
> {
> for (;;)
> malloc();
> }
>
> int main(void)
> {
> pthread_create(..., thread_func, ...);
> pthread_exit();
> }
>
> This process runs with the dead group-leader (PF_EXITING is set, ->mm == NULL).
> mem_cgroup_out_of_memory()->select_bad_process() can't see it due to
> task_in_mem_cgroup() check.
>
> Afaics
>
> - task_in_mem_cgroup() should use find_lock_task_mm() too
>
> - oom_kill_process() should check "PF_EXITING && p->mm",
> like select_bad_process() does.
>
Hm. I'd like to look into that when the next mmotm is shipped.
(too many pactches in flight..)
The problem is
for (walking each 'process')
if (task_in_mem_cgroup(p, memcg))
can't check 'p' containes threads belongs to given memcg because p->mm can
be NULL. So, task_in_mem_cgroup should call find_lock_task_mm() when
getting "mm" struct.
Thanks,
-Kame
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