Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over memory.high action

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On 8/17/20 10:30 AM, Chris Down wrote:
Astractly, I think this really overcomplicates the API a lot. If these are truly generally useful (and I think that remains to be demonstrated), they should be additions to the existing API, rather than a sidestep with prctl.
This patchset is derived from customer requests. With existing API, I suppose you mean the memory cgroup API. Right? The reason to use prctl() is that there are users out there who want some kind of per-process control instead of for a whole group of processes unless the users try to create one cgroup per process which is not very efficient.

I also worry about some other more concrete things:

1. Doesn't this allow unprivileged applications to potentially bypass    memory.high constraints set by a system administrator?
The memory.high constraint is for triggering memory reclaim. The new mitigation actions introduced by this patchset will only be applied if memory reclaim alone fails to limit the physical memory consumption. The current memory cgroup memory reclaim code will not be affected by this patchset.
2. What's the purpose of PR_MEMACT_KILL, compared to memory.max?
A user can use this to specify which processes are less important and can be sacrificed first instead of the other more important ones in case they are really in a OOM situation. IOW, users can specify the order where OOM kills can happen.
3. Why add this entirely separate signal delivery path when we already have eventfd/poll/inotify support, which makes a lot more sense for modern    applications?

Good question, I will look further into this to see if it can be applicable in this case.

Cheers,
Longman







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