RFR (S): 8242036: G1 HeapRegionRemSet::_n_coarse_entries could be a bool

[Kim Barrett]

> On Jul 23, 2020, at 8:29 AM, Albert Yang <albert.m.yang at oracle.com> wrote:
> 
> I misunderstood the original request from the internal discussion.
> 
> The variable is marked `volatile`, and access to it uses `Atomic::load/store`, or `Atomic::load_acquire/release_store` only when memory ordering is needed.
> 
> https://bugs.openjdk.java.net/browse/JDK-8242036
> 
> the complete patch:
> 
> http://cr.openjdk.java.net/~lkorinth/albert/8242036/2/
> 
> Tested: hotspot-gc
> 
> PS: My apologies for the inconvenience. 
> 
> /Albert

src/hotspot/share/gc/g1/heapRegionRemSet.cpp  
267     if (!_coarse_map.at(max_hrm_index)) {
268       _coarse_map.at_put(max_hrm_index, true);
269     }

The old code conditionalized on !_course_map.at() to avoid
incrementing _n_coarse_entries if the entry was already set.  That's
no longer needed.  It seems like it might be clearer to just do the
at_put unconditionally.  If so, also change the comment on line 264 to
say something like "Ensure the corresponding coarse bit is set."

src/hotspot/share/gc/g1/heapRegionRemSet.cpp  
273     assert(_coarse_map.at(max_hrm_index) == false, "No coarse entries");

+1 to Thomas's suggestion to not compare to false.

Sorry I didn't notice either of these previously.