RFR: 8303013: Always do remembered set verification during G1 Full GC

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that removes the `G1VerifyRSetsDuringFullGC` flag because it seems superfluous: if we are doing verification, we likely want to have all subsystems checked; now there is the argument that remset verification is somewhat expensive, and hence the reason for this flag. However I believe that the existing flags to control verification execution (`VerifyGCType`) are much better than this particular flag.

There is a `VerifyRememberedSets` flag available that is currently only used in Parallel GC that might be used here to control all remembered set verification; however I believe that if we do verification, we typically want all of it (and it can be toned down by `VerifyGCType` and friends). If you think it is useful, I can enable G1 to honour `VerifyRememberedSets` too (with a default of `true` and obviously only active if other verification is enabled).

Testing: tier1-3

Thanks,
  Thomas

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Commit messages:
 - Remove flag use
 - temporarily enable full verification

Changes: https://git.openjdk.org/jdk/pull/12781/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12781&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303013
  Stats: 12 lines in 3 files changed: 0 ins; 7 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12781.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12781/head:pull/12781

PR: https://git.openjdk.org/jdk/pull/12781