Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

On Mon, Aug 2, 2021 at 1:08 PM Suren Baghdasaryan [off-list ref] wrote:

On Mon, Aug 2, 2021 at 1:05 PM Shakeel Butt [off-list ref] wrote:

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On Mon, Aug 2, 2021 at 12:54 PM Suren Baghdasaryan [off-list ref] wrote:

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On Mon, Jul 26, 2021 at 6:44 AM Shakeel Butt [off-list ref] wrote:

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On Mon, Jul 26, 2021 at 12:27 AM Michal Hocko [off-list ref] wrote:

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Is process_mrelease on all of them really necessary? I thought that the
primary reason for the call is to guarantee a forward progress in cases
where the userspace OOM victim cannot die on SIGKILL. That should be
more an exception than a normal case, no?

I am thinking of using this API in this way: On user-defined OOM
condition, kill a job/cgroup and unconditionally reap all of its
processes. Keep monitoring the situation and if it does not improve go
for another kill and reap.

I can add additional logic in between kill and reap to see if reap is
necessary but unconditionally reaping is more simple.

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An alternative would be to have a cgroup specific interface for
reaping similar to cgroup.kill.

Could you elaborate?

I mentioned this in [1] where I was thinking if it makes sense to
overload cgroup.kill to also add the SIGKILLed processes in
oom_reaper_list. The downside would be that there will be one thread
doing the reaping and the syscall approach allows userspace to reap in
multiple threads. I think for now, I would go with whatever Suren is
proposing and we can always add more stuff if need arises.

[1] https://lore.kernel.org/containers/CALvZod4jsb6bFzTOS4ZRAJGAzBru0oWanAhezToprjACfGm+ew@mail.gmail.com/ (local)

Hi Folks,
So far I don't think there was any request for further changes.
Anything else you would want me to address or are we in a good shape
wrt this feature?
If so, would people who had a chance to review this patchset be
willing to endorse it with their Reviewed-by or Acked-by?

I think with Michal's suggestion to use a killable mmap lock, at least
I am good with the patch.

Ah, yes. Thanks for pointing this out! I'll replace mmap_read_lock()
with mmap_read_lock_killable(). Will post an updated version later
today.

Posted the next version at https://lore.kernel.org/patchwork/patch/1471403/