RFR: 8253332: ZGC: Make heap views reservation platform independent [v2]

[Stefan Karlsson]

On Fri, 18 Sep 2020 08:43:10 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp line 45:
>> 
>>> 43:   if (res != addr) {
>>> 44:     // Failed to reserve memory at the requested address
>>> 45:     munmap((void*)res, size);
>> 
>> No assert for `munmap` result? I don't care either way, but it would probably be nice to capture this.
>
> Also, hold on a sec. Shouldn't this path `return 0` too? Otherwise callers get the non-zero address that is effectively
> unusable.

For this particular function, the calling code is responsible for dealing with that. That is, I adopted the style used
by the windows reserve_contiguous_platform, instead of using the posix implementation. But it's probably nicer to not
leak out that address unnecessarily. I'll change this to the posix version instead.

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PR: https://git.openjdk.java.net/jdk/pull/236