RFR(S) JDK-8025526: VirtualSpace should support per-instance disabling of large pages

[Erik Helin]

On 2013-09-30, Mikael Gerdin wrote:
> Erik,
> 
> On 09/27/2013 05:10 PM, Erik Helin wrote:
> >Hi Mikael,
> >
> >what do you think about splitting the VirtualSpace::initialize method
> >into two methods:
> >- VirtualSpace::initialize
> >- VirtualSpace::initialize_with_granularity
> >
> >Then initialize would just call initialize_with_granularity like the
> >following:
> >
> >   bool VirtualSpace::initialize(ReservedSpace rs, size_t committed_size) {
> >     size_t granularity = os::page_size_for_regions(rs.size(), rs.size(), 1);
> >     return initialize_with_granularity(rs, committed_size, granularity);
> >   }
> >
> >   bool VirtualSpace::initialize_with_granularity(ReservedSpace rs,
> >     size_t committed_size, size_t granularity) {
> >     assert(granularity > 0, "Can't have 0 as granularity");
> >     // old initialize code
> >     _middle_alignment = granularity;
> >     // rest of old initialized code
> >   }
> >
> >This way, we get rid of the default argument and don't have to check if
> >max_commit_granularity == 0.
> 
> I like your suggestion.
> I've uploaded a second webrev which implements your suggestion.
> I had to update the test code so I re-ran the tests on all platforms.
> 
> New webrev: http://cr.openjdk.java.net/~mgerdin/8025526/webrev.1/

Besides from Thomas' comment about the default value for the method
parameter, this looks good! Thanks for also adding tests!

Erik

> /Mikael
> 
> >
> >Thanks,
> >Erik
> >
> >On 2013-09-27, Mikael Gerdin wrote:
> >>Hi,
> >>
> >>As part of ongoing work in getting Metaspace to properly enforce the
> >>MaxMetaspaceSize limit [JDK-8024547] we need to extend the
> >>VirtualSpace class to allow us to set the granularity at which
> >>VirtualSpace commits pages from the OS.
> >>
> >>Summary of changes:
> >>Extend VirtualSpace::initialize to take a parameter for setting the
> >>maximum commit granularity. The default value 0 keeps the previous
> >>behavior of using os::page_size_for_region to determine the
> >>granularity.
> >>Add unit tests for disabling and enabling large pages both at the
> >>ReservedSpace and the VirtualSpace level.
> >>
> >>Testing:
> >>JPRT run (includes running the new tests)
> >>
> >>Webrev: http://cr.openjdk.java.net/~mgerdin/8025526/webrev.0
> >>Bug link: https://bugs.openjdk.java.net/browse/JDK-8025526
> >>
> >>/Mikael
>