RFR [14]: 8232207: Linux os::available_memory re-reads cgroup configuration on every invocation

[Claes Redestad]

On 2019-10-16 06:08, David Holmes wrote:
>>> If the typical scenario is a static configuration then perhaps that
>>> would have been a better default. A fully adaptive mode (with the
>>> overheads that comes) sounds like something that should be an opt-in.
>>
>> +1 on fully adaptive mode should be opt-in.
>>
>> IIRC, the premise was that "we cannot prove that the config stays
>> static in all cases". Hence, the adaptive mode conclusion. I'm in no
>> way in that court, though.
> 
> Yes the underlying cgroup functionality allows for dynamism. The fact 
> some particular container framework chooses not to allow it is not 
> something we know a-priori or can readily detect. Until container 
> management APIs catch up we're stuck at assuming the worst-case - unless 
> we add flags to choose otherwise.

No. What we *must* do is to not regress the platform for existing users
and applications, and by making this assumption that the JVM should
default to re-reading cgroup settings all the time, that's just what
we've done. I now think we should treat this as the regression it is and
make the behavior to adapt to a change in constraints an opt-in.

/Claes