RFR(xs): 8245035: Clean up os::split_reserved_memory()

[coleen.phillimore at oracle.com]

http://cr.openjdk.java.net/~stuefe/webrevs/8245035--clean-up-os--split_reserved_memory()/webrev.00/webrev/src/hotspot/share/memory/virtualspace.hpp.udiff.html 


+ // If split==false, the resulting space will be just a hotspt-internal 
representation


typo: needs an 'o'

http://cr.openjdk.java.net/~stuefe/webrevs/8245035--clean-up-os--split_reserved_memory()/webrev.00/webrev/src/hotspot/share/runtime/os.cpp.udiff.html

I don't think we need a pd_ version to delegate to for this.  I guess 
it's a convention because the other memory allocation functions do it 
but maybe we can slowly end this bad convention.

This looks like a very nice cleanup.
Thank you!
Coleen

On 5/14/20 11:45 AM, Thomas Stüfe wrote:
> Hi,
>
> may I have reviews for this small cleanup please:
>
> jbs: https://bugs.openjdk.java.net/browse/JDK-8245035
> webrev:
> http://cr.openjdk.java.net/~stuefe/webrevs/8245035--clean-up-os--split_reserved_memory()/webrev.00/webrev/
>
> I need this as a preparation for
> https://bugs.openjdk.java.net/browse/JDK-8243535, which I'd like to review
> separately.
>
> os::split_reserved_memory() should be cleaned up a bit. It is used to split
> reserved memory regions in order to make them independent units. This only
> matters when releasing them, so after splitting these regions should be
> releasable independently from each other.
>
> This whole thing only matters on Windows, which is the only platform with a
> non-empty implementation, since virtual memory can only be released as a
> unit (opposed to mmap api, where sub regions can be unmapped individually).
>
> Improvements:
> - the interface should be commented
> - the "realloc" parameter can be removed. It has never not been true on all
> code paths - had it been, it would have been an error on windows resulting
> in loosing one of the two sides of the split.
> - the many non-windows implementations can be combined in posix.cpp.
>
> Thank you,
>
> Thomas