Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
On Mon, Nov 09, 2020 at 05:06:18PM +0100, Michal Hocko wrote: > On Mon 09-11-20 07:39:33, Minchan Kim wrote: > > On Mon, Nov 09, 2020 at 08:37:06AM +0100, Michal Hocko wrote: > > > On Fri 06-11-20 12:32:38, Minchan Kim wrote: > > > > It's hard to have some tests to be supposed to work under heavy > > > > memory pressure(e.g., injecting some memory hogger) because > > > > out-of-memory killer easily kicks out one of processes so system > > > > is broken or system loses the memory pressure state since it has > > > > plenty of free memory soon so. > > > > > > I do not follow the reasoning here. So you want to test for a close to > > > no memory available situation and the oom killer stands in the way > > > because it puts a relief? > > > > Yub, technically, I'd like to have consistent memory pressure to cause > > direct reclaims on proesses on the system and swapping in/out. > > > > > > > > Even though we could mark existing process's oom_adj to -1000, > > > > it couldn't cover upcoming processes to be forked for the job. > > > > > > Why? > > > > Thing is the system has out-of-control processes created on demand. > > so only option to prevent OOM is echo -1000 > `pidof the process` > > since they are forked. However, I have no idea when they are forked > > so should race with OOM with /proc polling and OOM is frequently > > ahead of me. > > I am still confused. Why would you want all/most processes to be hidden > from the oom killer? If one of processes in the system is killed, the memory pressure disappear. > > > > > This knob is handy to keep system memory pressure. > > > > > > This sounds like a very dubious reason to introduce a knob to cripple > > > the system. > > > > > > I can see some reason to control the oom handling policy because the > > > effect of the oom killer is really disruptive but a global on/off switch > > > sounds like a too coarse interface. Really what kind of production > > > environment would ever go with oom killer disabled completely? > > > > I don't think shipping production system will use it. It would be > > just testing only option. > > Then it doesn't really belong to the kernel IMHO. > > > My intention uses such heavy memory load to see various system behaviors > > before the production launching because it usually happens in real workload > > once we shipped but hard to generate such a corner case without artificial > > memory pressure. > > But changing the oom behavior will result in a completely different > system behavior. So you would be testing something that doesn't really > happen in any production system. Since OOM is not instantly reacted, it still provides a good chance how the system reacts on such memory pressure until someeone releases the memory. For example, Android already gives lots of system processes to -1000 which could effectively disable the OOM at certain point. > > > Any suggestion? > > Not really because I still do not understand your objective. You can > generate memory pressure and tune it up for specific testing scenario. > Sure there will be a some interference from the background noise (kernel > subsystems reacting to external events, processes created etc.) but why > that is a problem? This is normal to any running system. Putting more pressure from background processes is okay for the goal but not okay for relieving th memory pressure since we lost the testing environment.
Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
On Mon 09-11-20 07:39:33, Minchan Kim wrote: > On Mon, Nov 09, 2020 at 08:37:06AM +0100, Michal Hocko wrote: > > On Fri 06-11-20 12:32:38, Minchan Kim wrote: > > > It's hard to have some tests to be supposed to work under heavy > > > memory pressure(e.g., injecting some memory hogger) because > > > out-of-memory killer easily kicks out one of processes so system > > > is broken or system loses the memory pressure state since it has > > > plenty of free memory soon so. > > > > I do not follow the reasoning here. So you want to test for a close to > > no memory available situation and the oom killer stands in the way > > because it puts a relief? > > Yub, technically, I'd like to have consistent memory pressure to cause > direct reclaims on proesses on the system and swapping in/out. > > > > > Even though we could mark existing process's oom_adj to -1000, > > > it couldn't cover upcoming processes to be forked for the job. > > > > Why? > > Thing is the system has out-of-control processes created on demand. > so only option to prevent OOM is echo -1000 > `pidof the process` > since they are forked. However, I have no idea when they are forked > so should race with OOM with /proc polling and OOM is frequently > ahead of me. I am still confused. Why would you want all/most processes to be hidden from the oom killer? > > > This knob is handy to keep system memory pressure. > > > > This sounds like a very dubious reason to introduce a knob to cripple > > the system. > > > > I can see some reason to control the oom handling policy because the > > effect of the oom killer is really disruptive but a global on/off switch > > sounds like a too coarse interface. Really what kind of production > > environment would ever go with oom killer disabled completely? > > I don't think shipping production system will use it. It would be > just testing only option. Then it doesn't really belong to the kernel IMHO. > My intention uses such heavy memory load to see various system behaviors > before the production launching because it usually happens in real workload > once we shipped but hard to generate such a corner case without artificial > memory pressure. But changing the oom behavior will result in a completely different system behavior. So you would be testing something that doesn't really happen in any production system. > Any suggestion? Not really because I still do not understand your objective. You can generate memory pressure and tune it up for specific testing scenario. Sure there will be a some interference from the background noise (kernel subsystems reacting to external events, processes created etc.) but why that is a problem? This is normal to any running system. -- Michal Hocko SUSE Labs
Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
On Mon, Nov 09, 2020 at 08:37:06AM +0100, Michal Hocko wrote: > On Fri 06-11-20 12:32:38, Minchan Kim wrote: > > It's hard to have some tests to be supposed to work under heavy > > memory pressure(e.g., injecting some memory hogger) because > > out-of-memory killer easily kicks out one of processes so system > > is broken or system loses the memory pressure state since it has > > plenty of free memory soon so. > > I do not follow the reasoning here. So you want to test for a close to > no memory available situation and the oom killer stands in the way > because it puts a relief? Yub, technically, I'd like to have consistent memory pressure to cause direct reclaims on proesses on the system and swapping in/out. > > > Even though we could mark existing process's oom_adj to -1000, > > it couldn't cover upcoming processes to be forked for the job. > > Why? Thing is the system has out-of-control processes created on demand. so only option to prevent OOM is echo -1000 > `pidof the process` since they are forked. However, I have no idea when they are forked so should race with OOM with /proc polling and OOM is frequently ahead of me. > > > This knob is handy to keep system memory pressure. > > This sounds like a very dubious reason to introduce a knob to cripple > the system. > > I can see some reason to control the oom handling policy because the > effect of the oom killer is really disruptive but a global on/off switch > sounds like a too coarse interface. Really what kind of production > environment would ever go with oom killer disabled completely? I don't think shipping production system will use it. It would be just testing only option. My intention uses such heavy memory load to see various system behaviors before the production launching because it usually happens in real workload once we shipped but hard to generate such a corner case without artificial memory pressure. Any suggestion?
Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
On Fri 06-11-20 12:32:38, Minchan Kim wrote: > It's hard to have some tests to be supposed to work under heavy > memory pressure(e.g., injecting some memory hogger) because > out-of-memory killer easily kicks out one of processes so system > is broken or system loses the memory pressure state since it has > plenty of free memory soon so. I do not follow the reasoning here. So you want to test for a close to no memory available situation and the oom killer stands in the way because it puts a relief? > Even though we could mark existing process's oom_adj to -1000, > it couldn't cover upcoming processes to be forked for the job. Why? > This knob is handy to keep system memory pressure. This sounds like a very dubious reason to introduce a knob to cripple the system. I can see some reason to control the oom handling policy because the effect of the oom killer is really disruptive but a global on/off switch sounds like a too coarse interface. Really what kind of production environment would ever go with oom killer disabled completely? -- Michal Hocko SUSE Labs
Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
On Fri, Nov 06, 2020 at 12:46:47PM -0800, Randy Dunlap wrote: > Hi, > > Fix a few typos: > > On 11/6/20 12:32 PM, Minchan Kim wrote: > > --- > > Documentation/admin-guide/sysctl/vm.rst | 14 ++ > > include/linux/mm.h | 2 ++ > > include/linux/oom.h | 1 + > > kernel/sysctl.c | 9 + > > mm/oom_kill.c | 24 > > 5 files changed, 50 insertions(+) > > > > diff --git a/Documentation/admin-guide/sysctl/vm.rst > > b/Documentation/admin-guide/sysctl/vm.rst > > index f455fa00c00f..49dcedfaf0c0 100644 > > --- a/Documentation/admin-guide/sysctl/vm.rst > > +++ b/Documentation/admin-guide/sysctl/vm.rst > > @@ -694,6 +694,20 @@ is used in oom_kill_allocating_task. > > > > The default value is 0. > > > > +oom_kill_disable > > + > > + > > +This disables or enables OOM killing in out-of-memory situations. > > + > > +If this is set to one, the OOM killer is disabled so OOM kill never > > +hapens in out-of-memory situation. It could cause system dangerous > >happensIt could cause a dangerous system > > > +state due to memory allocation failure so user should be careful to > > careful when > > +use it. > >using it. > > > + > > +If this is set to zero, the OOM killer is enabled so OOM kill happens > > +in out-of-memory situations. > > + > > +The default value is 0. > > > > overcommit_kbytes > > = > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 8b84661a6410..0f48cdeeb1e7 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > > #ifdef CONFIG_NUMA > > /** > > * oom_cpuset_eligible() - check task eligiblity for kill > > eligibility > > but that's not in your patch, so don't bother with it. :) Sure, I will resend it with fixing after waiting some feedback. Thanks for the review, Randy.
Re: [PATCH] mm: introduce oom_kill_disable sysctl knob
Hi, Fix a few typos: On 11/6/20 12:32 PM, Minchan Kim wrote: > --- > Documentation/admin-guide/sysctl/vm.rst | 14 ++ > include/linux/mm.h | 2 ++ > include/linux/oom.h | 1 + > kernel/sysctl.c | 9 + > mm/oom_kill.c | 24 > 5 files changed, 50 insertions(+) > > diff --git a/Documentation/admin-guide/sysctl/vm.rst > b/Documentation/admin-guide/sysctl/vm.rst > index f455fa00c00f..49dcedfaf0c0 100644 > --- a/Documentation/admin-guide/sysctl/vm.rst > +++ b/Documentation/admin-guide/sysctl/vm.rst > @@ -694,6 +694,20 @@ is used in oom_kill_allocating_task. > > The default value is 0. > > +oom_kill_disable > + > + > +This disables or enables OOM killing in out-of-memory situations. > + > +If this is set to one, the OOM killer is disabled so OOM kill never > +hapens in out-of-memory situation. It could cause system dangerous happensIt could cause a dangerous system > +state due to memory allocation failure so user should be careful to careful when > +use it. using it. > + > +If this is set to zero, the OOM killer is enabled so OOM kill happens > +in out-of-memory situations. > + > +The default value is 0. > > overcommit_kbytes > = > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 8b84661a6410..0f48cdeeb1e7 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > #ifdef CONFIG_NUMA > /** > * oom_cpuset_eligible() - check task eligiblity for kill eligibility but that's not in your patch, so don't bother with it. :) -- ~Randy
