On Tue 24-10-17 13:23:30, Johannes Weiner wrote: > On Tue, Oct 24, 2017 at 06:22:13PM +0200, Michal Hocko wrote: [...] > > What would prevent a runaway in case the only process in the memcg is > > oom unkillable then? > > In such a scenario, the page fault handler would busy-loop right now. > > Disabling oom kills is a privileged operation with dire consequences > if used incorrectly. You can panic the kernel with it. Why should the > cgroup OOM killer implement protective semantics around this setting? > Breaching the limit in such a setup is entirely acceptable. > > Really, I think it's an enormous mistake to start modeling semantics > based on the most contrived and non-sensical edge case configurations. > Start the discussion with what is sane and what most users should > optimally experience, and keep the cornercases simple. I am not really seeing your concern about the semantic. The most important property of the hard limit is to protect from runaways and stop them if they happen. Users can use the softer variant (high limit) if they are not afraid of those scenarios. It is not so insane to imagine that a master task (which I can easily imagine would be oom disabled) has a leak and runaway as a result. We are not talking only about the page fault path. There are other allocation paths to consume a lot of memory and spill over and break the isolation restriction. So it makes much more sense to me to fail the allocation in such a situation rather than allow the runaway to continue. Just consider that such a situation shouldn't happen in the first place because there should always be an eligible task to kill - who would own all the memory otherwise? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
