Hello. On Thu, Aug 01, 2024 at 07:40:10PM GMT, Lance Yang <ioworker0@xxxxxxxxx> wrote: > However, if the child cgroup doesn't exist and we add a process to the 'test' > cgroup, then attempt to create a large file(2GB) using dd, we won't encounter > an OOM error; everything works as expected. That's due to the way how effective protections are calculated, see [1]. If reclaim target is cgroup T, then it won't enjoy protection configured on itself, whereas the child of T is subject of ancestral reclaim hence the protection applies. That would mean that in your 1st demo, it is test/memory.max that triggers reclaim and then failure to reclaim from test/test-child causes OOM in test. That's interesting since the (same) limit of test-child/memory.max should be evaluated first. I guess it is in your example there are actually two parallel processes (1321 and 1324) so some charges may randomly propagate to the upper test/memory.max limit. As explained above, the 2nd demo has same reclaim target but due to no nesting, protection is moot. I believe you could reproduce with merely test/memory.max test-child/memory.min > Hmm... I'm a bit confused about that. I agree, the calculation of effective protection wrt reclaim target can be confusing. The effects you see are documented for memory.min: > Putting more memory than generally available under this > protection is discouraged and may lead to constant OOMs. HTH, Michal [1] https://lore.kernel.org/all/20200729140537.13345-2-mkoutny@xxxxxxxx/
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