RFR (S): 8067438: Add test to verify minimal heap size

[Thomas Schatzl]

Hi,

On Thu, 2015-01-08 at 08:44 +0100, Bengt Rutisson wrote:
> On 2015-01-07 21:35, Thomas Schatzl wrote:
> > Hi,
> >
> > On Wed, 2015-01-07 at 21:07 +0100, Bengt Rutisson wrote:
> >> On 1/7/15 5:04 PM, Lindenmaier, Goetz wrote:
> >>> Hi Bengt,
> >>>
> >>> I had to add the new path to this line:
> >>>    * @library /testlibrary /testlibrary/whitebox  /../../test/lib
> >> Right. I was using a repository that hadn't been updated to include this
> >> change yet. Good that you noticed it and could handle it.
> >>
> >>> But then it works fine on the machine with 64K pages.
> >> Great to hear! And my testing on our platforms also passed.
> > Please add a comment about the 512 magic number in the test, and that we
> > assume that the heap constraint of page size * 512 is at this time the
> > largest heap sizing constraint. I.e. that this formula is a
> > simplification of the actual calculation.
> >
> > Did you also test on a machine with large pages with parallel gc? Iirc
> > there has been some constraint that e.g. parallel gc needs at least
> > three (or four?) full pages for its heap, one for each of its spaces.
> >
> > So I am not sure if this test as is is sufficiently robust.
> 
> We don't use large pages for such small heaps. See this in 
> Arguments::finalize_vm_init_args():
> 
> 
>    if (FLAG_IS_DEFAULT(UseLargePages) &&
>        MaxHeapSize < LargePageHeapSizeThreshold) {
>      // No need for large granularity pages w/small heaps.
>      // Note that large pages are enabled/disabled for both the
>      // Java heap and the code cache.
>      FLAG_SET_DEFAULT(UseLargePages, false);
>    }
> 
> LargePageHeapSizeThreshold is 128 MB and since my test runs with -Xmx2m 
> (which admittedly can be aligned up to 32 mb) I think we will never use 
> large pages.
> 
> But I'll do an explicit run on a large page enabled machine with 
> ParallelGC just to make sure.

Okay :) But what if somebody sets -XX:+UseLargePages intentionally for a
test run?

Potentially we will need to exclude this case then.

Thanks,
  Thomas