On Thu, 22 Aug 2024 19:50:21 GMT, Albert Mingkun Yang <ay...@openjdk.org> wrote:
>> Roman Kennke has updated the pull request incrementally with one additional >> commit since the last revision: >> >> Fix hash shift for 32 bit builds > > src/hotspot/share/gc/shared/gcForwarding.hpp line 36: > >> 34: * Implements forwarding for the full-GCs of Serial, Parallel, G1 and >> Shenandoah in >> 35: * a way that preserves upper N bits of object mark-words, which contain >> crucial >> 36: * Klass* information when running with compact headers. The encoding is >> similar to > > This doc suggests this forwarding is only for compact-header so I wonder if > we can check `UseCompactObjectHeaders` directly instead of heap-size in > `GCForwarding::initialize`. Right. The original implementation was more complex and then the consensus was to not sprinkle UseCompactHeaders all over the place, but with that new/simpler implementation it makes sense to simply check the UCOH flag. > src/hotspot/share/gc/shared/gcForwarding.hpp line 40: > >> 38: * heap-base, shifts that difference into the right place, and sets the >> lowest two >> 39: * bits (to indicate 'forwarded' state as usual). >> 40: */ > >> "can use 40 bits for forwardee encoding. That's enough for 8TB of heap." > > I feel this 8T-constraint is significant and should be in the doc. Done. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1750264571 PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1750265026
