RFR: 8224817: Implementation of JEP 364: ZGC on macOS

[Per Liden]

Some suggested adjustments, already discussed with Erik off-line:

http://cr.openjdk.java.net/~pliden/8224817/webrev.review.0

/Per

On 10/28/19 5:11 PM, Erik Österlund wrote:
> Hi,
> 
> After some internal discussions with Per and Stefan, some refactorings 
> have been made:
> 
> 1) Use mmap consistently wherever possibly, instead of mach_vm_map, for 
> consistency. And only use mach_vm_remap from a wrapper function to map 
> in views.
> 2) Move the pmem segments up one level so that producer and consumer of 
> the segments is on the same level, and let the virtual "file" know only 
> about offsets.
> 3) Minor polishing.
> 
> Incremental:
> http://cr.openjdk.java.net/~eosterlund/8224817/webrev.00..01/
> 
> Full:
> http://cr.openjdk.java.net/~eosterlund/8224817/webrev.01/
> 
> Thanks,
> /Erik
> 
> On 2019-10-24 12:38, erik.osterlund at oracle.com wrote:
>> Hi,
>>
>> Now that some curling has been performed, paving way for this patch:
>>
>>     8229027: Improve how JNIHandleBlock::oops_do distinguishes oops 
>> from non-oops
>>     8229278: Improve hs_err location printing to assume less about GC 
>> internals
>>     8229189: Improve JFR leak profiler tracing to deal with 
>> discontiguous heaps
>>     8224815: Remove non-GC uses of CollectedHeap::is_in_reserved()
>>     8224820: ZGC: Support discontiguous heap reservations
>>
>> ...the remaining thing to do is plugging in a few platform specific 
>> ZGC files. This patch does that.
>> Decided to go with mach_vm_map/mach_vm_remap to implement 
>> multi-mapping. Previously I didn't want to do that as I couldn't 
>> figure out how to mach_vm_remap memory on top of reserved VA (acquired 
>> using mmap). But apparently VM_FLAGS_OVERWRITE was the missing 
>> ingredient there. With that in place, dodging the terrible ftruncate 
>> implementation on macOS seemed like a good idea. That also implies 
>> this port supports large pages (unlike other GCs on macOS today). Yay!
>>
>> CR:
>> http://cr.openjdk.java.net/~eosterlund/8224817/webrev.00/
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8229358
>>
>> Thanks,
>> /Erik
>