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
