oom-kill: give the dying task a higher priority
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From: KOSAKI Motohiro on 2 Jun 2010 10:00 > > @@ -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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Luis Claudio R. Goncalves on 2 Jun 2010 10:40 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 -- [ Luis Claudio R. Goncalves Bass - Gospel - RT ] [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: David Rientjes on 2 Jun 2010 17:20 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: KOSAKI Motohiro on 2 Jun 2010 19:40 > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Minchan Kim on 2 Jun 2010 21:00
On Thu, Jun 3, 2010 at 8:36 AM, KOSAKI Motohiro <kosaki.motohiro(a)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(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |