RFR: 8213175 - MaxHeapSize refuses to go over 32178700288 when running in a docker container

Thomas Schatzl thomas.schatzl at oracle.com
Tue Mar 19 21:42:36 UTC 2019


Hi,

  first, sorry for the delay in answering.

On Thu, 2019-03-14 at 16:51 -0400, Bob Vandette wrote:
> Thanks for the feedback Thomas. 
> 
> You are correct that the change I implemented will cause us to select
> non coop mode rather than cap the size of the heap.  This was not my
> intention.  This Heap Size flag processing in Hotspot is non
> intuitive.  We make a decision to turn on UseCompressedOops based on
> the default value of MaxHeapSize (96MB on x64) but then look at the
> real amount of memory in the system and then assume we want to keep
> coops on rather than use a potentially much larger heap.

Because for most applications coops (and a smaller heap) is preferable
to a large heap.
This is the case typically used by people that just want to run a small
application.

> My implementation does all the heap sizing and then determines if we
> can enable CompressedOops based on the size we determined.
> 
> The change that I had hoped to implement only disables coop mode if
> the user specifies MaxRAMPercentage.  The justification is that if
> the user specified this flag, they want this behavior over other
> conflicting ones.
> 
> I’ll try to refine my implementation to end up with a less invasive
> solution. 

Okay.

> 
> See more comments below ...
> 
> > On Mar 14, 2019, at 7:19 AM, Thomas Schatzl <
> > thomas.schatzl at oracle.com> wrote:
> > 
> > Hi,
> > 
[...]
> > This is a significant externally visible change to behavior, so
> > this needs a CSR regardless of pre-existing intended behavior or
> > not.
> 
> I will file a CSR once I settle on an implementation.

That's fine.

[...]
> > This RFR does not give performance numbers. Did you check for
> > performance regressions in our benchmark suites?
> 
> Please send me a private email on how to run the benchmarks you
> are concerned with.

Okay.

Thanks,
  Thomas




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