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January 2024

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Missing gc time in zgc generational logging
by Mike Millson 09 Jan '24

09 Jan '24

There seems to be a lot of missing gc time in the jdk21 zgc generational logging. Following is an example (complete log attached). The gc time below is .234ms, and the safepoint is 2.7ms (1900085+806967+4204/10^6). It's over an order of magnitude off. [2023-12-12T10:20:45.260+0200][info][gc,phases ] GC(34) y: Pause Mark Start 0.234ms [2023-12-12T10:20:45.260+0200][info][safepoint ] Safepoint "ZMarkStartYoung", Time since last: 9642266719 ns, Reaching safepoint: 1900085 ns, Cleanup: 4204 ns, At safepoint: 806967 ns, Total: 2711256 ns Thank you, Mike

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RFR: 8306656: Fix age table logging
by Erik Helin 02 Jan '24

02 Jan '24

Hey all, please review this patch that updates the age table logging. The logging now looks like: [1.946s][info][gc,reloc ] GC(22) y: Age Table: [1.946s][info][gc,reloc ] GC(22) y: Live Small Medium Large [1.946s][info][gc,reloc ] GC(22) y: Eden 0M -> 0M 300 -> 300 0 -> 0 0 -> 0 [1.946s][info][gc,reloc ] GC(22) y: Survivor 1 0M -> 0M 2 -> 2 0 -> 0 0 -> 0 [1.946s][info][gc,reloc ] GC(22) y: Survivor 2 0M -> 0M 1 -> 0 0 -> 0 0 -> 0 [1.946s][info][gc,reloc ] GC(22) y: Survivor 3 0M -> 0M 1 -> 1 0 -> 0 0 -> 0 [1.946s][info][gc,reloc ] GC(22) y: Survivor 4 0M -> 0M 0 -> 1 0 -> 0 0 -> 0 The first column is the size of the live objects with the given age and how that has changed since the previous collection. The remaining columns are the number of pages of the given age and how those have changed from the previous collection to the current one (so the format is `<previous> -> <current>`). This makes it easy to spot a change in behavior in objects' lifetimes from one collection to another: if objects have similar lifetimes compared to the previous collection then the distribution of pages should be similar between the current collection and the previous collection. _Note_: I would like to make the table adapt to live sizes smaller than one megabyte, but that should probably be done for the logging as a whole, not just for the age table. I also cleaned up some minor stuff as I went along. Testing: - [x] Tier 1-3 (macOS-aarch64, Windows-x64, Linux-x64, Linux-aarch64) - [x] Local testing on macOS-aarch64 Thanks, Erik ------------- Commit messages: - Rework age table logging Changes: https://git.openjdk.org/zgc/pull/19/files Webrev: https://webrevs.openjdk.org/?repo=zgc&pr=19&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8306656 Stats: 200 lines in 10 files changed: 104 ins; 52 del; 44 mod Patch: https://git.openjdk.org/zgc/pull/19.diff Fetch: git fetch https://git.openjdk.org/zgc.git pull/19/head:pull/19 PR: https://git.openjdk.org/zgc/pull/19

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