Messages in this thread | | | Date | Thu, 3 Jun 2010 09:52:49 +0900 | Subject | Re: [RFC] oom-kill: give the dying task a higher priority | From | 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.
-- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |