Question regarding JEP 8204089 Timely Reducing Unused Committed Memory

[Thomas Schatzl]

Hi,

  some comments to your questions; note that the functionality and the
JEP are still very much in a flux, so things are going change. Looking
at the responses so far, we all appreciate your input.

Rodrigo and Ruslan were proposing this feature, so they are the source
for authorative answers; apart from being interested in this feature
for G1, I am only helping with the process (and missing access rights
for them) :)

On Fri, 2018-06-01 at 04:41 +0000, Sunny Chan, CLSA wrote:
> (resending for hotspot-gc-dev)
>  
> Hello,
>  
> I have a number of question about the proposed changes for the JEP
> and I would like to make the following suggestions and comments
>  
> 1)      Are we planning to make this change the default behavior for
> G1? Or this is an optional switch for people who runs in a container
> environment?

Optional. Added to the JEP text.

> 2)      In a trading systems, sometimes there are period of
> quiescence and then suddenly a burst of activity towards market close
> or market event. The loadavg you suggest to “monitor” the activity in
> the system only reports up to 14mins and it might not necessary a
> good measure for this type of applications, especially you would
> trigger a Full GC

The idea is to have this feature off by default from what I understand.

> 3)      You haven’t fill in the details for “The GCFrequency value is
> ignored and therefore, i.e., no full collection is triggered, if:”

I removed that sentence, some copy&paste error. The details on when the
 VM is going to detect idleness, see above. Also Ruslan already
detailed them a bit more.

> 4)      If we are trigging full GC with this we should make sure the
> GC reason is populated and log properly in the GC log so we can track
> it down.

Noted.

> 5)      I have not heard of J9 Gencon/Shenandoah providing similar
> functionality. Can you point me to further documentation on which
> feature you model upon?

This has already been answered in this thread. I added some comments to
the JEP to be incorporated soon.

Thanks,
  Thomas