RFR (S): 8079208: gc/g1/TestLargePageUseForAuxMemory.java fails due to not considering page allocation granularity for setup

[Thomas Schatzl]

Hi,

On Wed, 2015-05-13 at 14:50 -0700, Jon Masamitsu wrote:
> 
> On 5/13/2015 8:03 AM, Thomas Schatzl wrote:
> > Hi all,
> >
> >    can I have reviews for the following test fix: the problem is that
> > during test setup, when trying to find the heap size where large pages
> > are just not used, the code subtracts a fixed value from the one known
> > to use large pages for the card table.
> >
> > The problem is that this fixed value is too small to have an impact on
> > the actual size of the card table, i.e. the code rounds up by the OS'es
> > allocation granularity. That causes it to use the same size as before,
> > where it will then use large pages anyway and fail the test.
> >
> > That fixed value has been just large enough to cover regular page size.
> >
> > Also, the only OS that has different allocation granularities and
> > (small) page sizes is Windows. Further on Windows, large pages (and the
> > test is only executed then) are only available when the user runs as
> > Administrator (or has the corresponding capability to lock pages in
> > memory).
> Thomas,
> 
> Is there a change for this need to run the test with sufficient privileges?

There is no way I know of to specify the requirement of this privilege
anywhere in jprt. Any idea?

In other test frameworks you could require large-page support for the
machine.

> > In this case the test fails.
> >
> > The change fixes this by making sure that this value to subtract from
> > the original heap size is exactly the size that avoids this rounding.
> 
> The fix to the test looks good.
> 
> Is it important to the test that the amount subtracted be the minimum
> needed to disable large pages?  I mean, is the test less useful if
> twice that minimum was subtracted?

It will not test that the expected cross-over between using large pages
and small pages is at exactly at that particular heap size. This seems
to test more than when subtracting any random value.

However I can add this test case too.

> For
> 
> >   119             final long heapSizeDiffForCardTable = Math.max(Math.max(allocGranularity * cardSize, HEAP_REGION_SIZE), largePageSize);
> 
> would this description be correct?
> 
> // Minimum change in heap size that will disable large pages for the 
> card table if subtracted from
> // the heap size.  Increasing the heap by this amount should not change 
> the use of large pages
> // for the card table.
> 
> If yes, would you mind adding it.

Will do, thanks.

Thomas