On Wed, Mar 16, 2016 at 01:13:29PM -0700, Johannes Weiner wrote:

On Wed, Mar 16, 2016 at 06:15:09PM +0300, Vladimir Davydov wrote:

quoted

On Tue, Mar 15, 2016 at 10:18:48PM -0700, Johannes Weiner wrote:

quoted

On Fri, Mar 11, 2016 at 12:19:31PM +0300, Vladimir Davydov wrote:

...

quoted

quoted

Come to think of it, shouldn't we restore the old limit and return EBUSY
if we failed to reclaim enough memory?

I suspect it's very rare that it would fail. But even in that case
it's probably better to at least not allow new charges past what the
user requested, even if we can't push the level back far enough.

It's of course good to set the limit before trying to reclaim memory,
but isn't it strange that even if the cgroup's memory can't be reclaimed
to meet the new limit (tmpfs files or tasks protected from oom), the
write will still succeed? It's a rare use case, but still.

It's not optimal, but there is nothing we can do about it, is there? I
don't want to go back to the racy semantics that allow the application
to balloon up again after the limit restriction fails.

quoted

I've one more concern regarding this patch. It's about calling OOM while
reclaiming cgroup memory. AFAIU OOM killer can be quite disruptive for a
workload, so is it really good to call it when normal reclaim fails?

W/o OOM killer you can optimistically try to adjust memory.max and if it
fails you can manually kill some processes in the container or restart
it or cancel the limit update. With your patch adjusting memory.max
never fails, but OOM might kill vital processes rendering the whole
container useless. Wouldn't it be better to let the user decide if
processes should be killed or not rather than calling OOM forcefully?

Those are the memory.max semantics, though. Why should there be a
difference between the container growing beyond the limit and the
limit cutting into the container?

If you don't want OOM kills, set memory.high instead. This way you get
the memory pressure *and* the chance to do your own killing.

Fair enough.

Thanks,
Vladimir

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