RFR: 8268122: Add specific gc cause for G1 full collections

Stefan Johansson sjohanss at openjdk.java.net
Fri Jun 4 11:42:11 UTC 2021


Please review this change to add a new GC cause for GC Full collections that are caused by a prior collection not being able to free up enough space.

**Summary**
During the review of PR #3143 it got pretty clear that reusing the Young GC cause for a following Full GC is not always good. A solution for this is to add a new GC cause that is used if a young collection can't free up enough space. This cause will not be used for other explicit Full GCs, like a call to `System.gc()`.

The would result in a change from:

[13,276s][info][gc             ] GC(71) Pause Young (Normal) (G1 Evacuation Pause) 3096M->3096M(3100M) 1,159ms
[13,644s][info][gc             ] GC(72) Pause Full (G1 Evacuation Pause) 3096M->3096M(3100M) 368,157ms

to:

[18,454s][info][gc             ] GC(84) Pause Young (Normal) (G1 Evacuation Pause) 3096M->3096M(3100M) 1,312ms
[18,815s][info][gc             ] GC(85) Pause Full (G1 Compaction Pause) 3096M->3096M(3100M) 360,737ms


This PR is currently based in PR #4342, where we slightly change how Full GCs are scheduled if a Younc GC can't free up enough space.

**Testing**
I've tested this change together with PR #4342 and tier1-3 looks good. Also done manual testing making sure the GC-cause is used correctly.

-------------

Depends on: https://git.openjdk.java.net/jdk/pull/4342

Commit messages:
 - G1 Compaction Pause

Changes: https://git.openjdk.java.net/jdk/pull/4357/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4357&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268122
  Stats: 6 lines in 3 files changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4357.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4357/head:pull/4357

PR: https://git.openjdk.java.net/jdk/pull/4357


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