On Mon, 14 Nov 2022 10:15:41 GMT, Erik Österlund <[email protected]> wrote:
>> The current loom code makes some assumptions about GC that will not work
>> with generational ZGC. We should make this code more GC agnostic, and
>> provide a better interface for talking to the GC.
>>
>> In particular,
>> 1) All GCs have a way of encoding oops inside of the heap differently to
>> oops outside of the heap. For non-ZGC collectors, that is compressed oops.
>> For ZGC, that is colored pointers. With generational ZGC, pointers on-heap
>> will be colored and pointers off-heap will be "colorless". So we need to
>> generalize encoding and decoding of oops in the heap, for loom.
>>
>> 2) The cont_oop is located on a stack. In order to access it we need to
>> start_processing on that thread, if it isn't the current thread. This
>> happened to work so far for ZGC, because the stale pointers had enough
>> colors. But with generational ZGC, these on-stack oops will be colorless, so
>> we have to be more accurate here and ensure processing really has started on
>> any thread that cont_oop is used on. To make life a bit easier, I'm moving
>> the oop processing responsibility for these oops to the thread instead.
>> Currently there is no more than one of these, so doing it lazily per frame
>> seems a bit overkill.
>>
>> 3) Refactoring the stack chunk allocation code
>>
>> Tested with tier1-5 and manually running Skynet. No regressions detected. We
>> have also been running with this (yet a slightly different backend) in the
>> generational ZGC repo for a while now.
>
> Erik Österlund has updated the pull request incrementally with one additional
> commit since the last revision:
>
> Fix verification and RISC-V support
Looks good to me. I wrote parts of this code, so I want wan extra Reviewer on
this patch.
I wonder if we should rename the title to something less ZGC specific?
src/hotspot/share/prims/stackwalk.hpp line 102:
> 100: Method* method() override { return _vfst.method(); }
> 101: int bci() override { return _vfst.bci(); }
> 102: oop cont() override { return _vfst.continuation(); }
Revert
-------------
Marked as reviewed by stefank (Reviewer).
PR: https://git.openjdk.org/jdk/pull/11111
