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

[Thomas Schatzl]

Hi,

On 24.10.19 17:47, Per Liden wrote:
> Hi,
> 
> On 10/24/19 12:38 PM, 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!

Not completely related and not a review:

Please file an RFE with a link to this mechanism. It would be nice to do 
such changes in a generic way so that all collectors benefit in the 
future, not just one.

Its confusing as already is with one collector supporting this and other 
collectors supporting that, adding to that is not nice.

Thanks,
   Thomas