8364081: Shenandoah & GenShen logging improvement #26469

rgithubli · 2025-07-25T01:30:59Z

Fix missing increment_total_collections usages in Shenandoah (otherwise, the invocation count is always 0 as shown in #26272 overview).

Also added some generational information for generational shenandoah logging.

Shenandoah logging samples:

######################
Shenandoah - Beore GC
######################
[0.161s][debug][gc,heap      ] GC(0) Heap Before GC invocations=0 (full 0):
[0.161s][debug][gc,heap      ] GC(0)  Shenandoah Heap
[0.161s][debug][gc,heap      ] GC(0)    100M max, 100M soft max, 100M committed, 40312K used
[0.161s][debug][gc,heap      ] GC(0)   400 x 256K regions
[0.161s][debug][gc,heap      ] GC(0)  Status: not cancelled
[0.161s][debug][gc,heap      ] GC(0)  Reserved region:
[0.161s][debug][gc,heap      ] GC(0)   - [0x00000000f9c00000, 0x0000000100000000) 
[0.161s][debug][gc,heap      ] GC(0)  Collection set:
[0.161s][debug][gc,heap      ] GC(0)   - map (vanilla): 0x0000000000004e70
[0.161s][debug][gc,heap      ] GC(0)   - map (biased):  0x0000000000001000
[0.161s][debug][gc,heap      ] GC(0) 
[0.161s][debug][gc,metaspace ] GC(0) Metaspace Before GC invocations=0 (full 0):
[0.161s][debug][gc,metaspace ] GC(0)  Metaspace       used 86K, committed 320K, reserved 1114112K
[0.161s][debug][gc,metaspace ] GC(0)   class space    used 3K, committed 128K, reserved 1048576K

######################
Shenandoah - After GC
######################
[2.179s][debug][gc,heap        ] GC(9) Heap After GC invocations=17 (full 7):
[2.179s][debug][gc,heap        ] GC(9)  Shenandoah Heap
[2.179s][debug][gc,heap        ] GC(9)    100M max, 100M soft max, 100M committed, 97113K used
[2.179s][debug][gc,heap        ] GC(9)   400 x 256K regions
[2.179s][debug][gc,heap        ] GC(9)  Status: not cancelled
[2.179s][debug][gc,heap        ] GC(9)  Reserved region:
[2.179s][debug][gc,heap        ] GC(9)   - [0x00000000f9c00000, 0x0000000100000000) 
[2.179s][debug][gc,heap        ] GC(9)  Collection set:
[2.179s][debug][gc,heap        ] GC(9)   - map (vanilla): 0x0000000000004e70
[2.179s][debug][gc,heap        ] GC(9)   - map (biased):  0x0000000000001000
[2.179s][debug][gc,heap        ] GC(9) 
[2.179s][debug][gc,metaspace   ] GC(9) Metaspace After GC invocations=17 (full 7):
[2.179s][debug][gc,metaspace   ] GC(9)  Metaspace       used 125K, committed 320K, reserved 1114112K
[2.179s][debug][gc,metaspace   ] GC(9)   class space    used 4K, committed 128K, reserved 1048576K

Generational Shenandoah logging samples

######################
Generational Shenandoah - Beore GC
######################
[0.212s][debug][gc,heap      ] GC(0) Heap Before GC invocations=0 (full 0):
[0.212s][debug][gc,heap      ] GC(0)  Generational Shenandoah Heap
[0.212s][debug][gc,heap      ] GC(0)   Young:
[0.212s][debug][gc,heap      ] GC(0)    100M max, 39686K used
[0.212s][debug][gc,heap      ] GC(0)   Old:
[0.212s][debug][gc,heap      ] GC(0)    0B max, 0B used
[0.212s][debug][gc,heap      ] GC(0)   Entire heap:
[0.212s][debug][gc,heap      ] GC(0)    100M soft max, 100M committed
[0.212s][debug][gc,heap      ] GC(0)  Status: not cancelled
[0.212s][debug][gc,heap      ] GC(0)  Reserved region:
[0.212s][debug][gc,heap      ] GC(0)   - [0x00000000f9c00000, 0x0000000100000000) 
[0.212s][debug][gc,heap      ] GC(0)  Collection set:
[0.212s][debug][gc,heap      ] GC(0)   - map (vanilla): 0x0000000000004e70
[0.212s][debug][gc,heap      ] GC(0)   - map (biased):  0x0000000000001000
[0.212s][debug][gc,heap      ] GC(0) 
[0.212s][debug][gc,metaspace ] GC(0) Metaspace Before GC invocations=0 (full 0):
[0.212s][debug][gc,metaspace ] GC(0)  Metaspace       used 153K, committed 384K, reserved 1114112K
[0.212s][debug][gc,metaspace ] GC(0)   class space    used 3K, committed 128K, reserved 1048576K

######################
Generational Shenandoah - After GC
######################
[1.752s][debug][gc,heap        ] GC(18) Heap After GC invocations=19 (full 3):
[1.752s][debug][gc,heap        ] GC(18)  Generational Shenandoah Heap
[1.752s][debug][gc,heap        ] GC(18)   Young:
[1.752s][debug][gc,heap        ] GC(18)    3328K max, 2883K used
[1.752s][debug][gc,heap        ] GC(18)   Old:
[1.752s][debug][gc,heap        ] GC(18)    99072K max, 98060K used
[1.752s][debug][gc,heap        ] GC(18)   Entire heap:
[1.752s][debug][gc,heap        ] GC(18)    100M soft max, 100M committed
[1.752s][debug][gc,heap        ] GC(18)  Status: young marking, cancelled
[1.752s][debug][gc,heap        ] GC(18)  Reserved region:
[1.752s][debug][gc,heap        ] GC(18)   - [0x00000000f9c00000, 0x0000000100000000) 
[1.752s][debug][gc,heap        ] GC(18)  Collection set:
[1.752s][debug][gc,heap        ] GC(18)   - map (vanilla): 0x0000000000004e70
[1.752s][debug][gc,heap        ] GC(18)   - map (biased):  0x0000000000001000
[1.752s][debug][gc,heap        ] GC(18) 
[1.752s][debug][gc,metaspace   ] GC(18) Metaspace After GC invocations=19 (full 3):
[1.752s][debug][gc,metaspace   ] GC(18)  Metaspace       used 209K, committed 448K, reserved 1114112K
[1.752s][debug][gc,metaspace   ] GC(18)   class space    used 7K, committed 128K, reserved 1048576K

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Issue

JDK-8364081: Shenandoah & GenShen logging improvement (Enhancement - P4)

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William Kemper (@earthling-amzn - Reviewer)

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bridgekeeper · 2025-07-25T01:31:33Z

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openjdk · 2025-07-25T01:32:20Z

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8364081: Shenandoah & GenShen logging improvement

Reviewed-by: wkemper

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At the time when this comment was updated there had been 10 new commits pushed to the master branch:

e756c0d: 8361726: Shenandoah: More detailed evacuation instrumentation
89fe586: 8363837: Make StubRoutines::crc_table_adr() into platform-specific method
9e209fe: 8364110: Remove unused methods in GCCause
... and 7 more: https://git.openjdk.org/jdk/compare/971ea23c95764e11ed234f657eb28ba7c51862c5...master

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openjdk · 2025-07-25T01:33:02Z

@rgithubli The following labels will be automatically applied to this pull request:

hotspot-gc
shenandoah

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-07-25T14:12:04Z

Webrevs

01: Full - Incremental (1d51fcff)
00: Full (235aac2f)

openjdk · 2025-07-25T15:52:50Z

@rgithubli Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

earthling-amzn

LGTM. Thanks for fixing this.

ysramakrishna

I am wondering if we could just hoist the incrementing of the collections count to run_gc_cycle() which would normally take care of everything at once in one place, with the option true for stw and full cases.

It would probably miss the upgrade to full at a degen. We could either overcount by incrementing at the point of upgrade to full or gloss over it. I'd do the former (which is what I believe your degen upgrade to full does here).

(The other, perhaps arguably (or subjectively) better semantics, for full in the case of concurrent collectors is to conflate degens with full, treating both as a kind of failure of concurrent mode.

The problem is that the "total collections & full collections" terminology is inadequate when we have concurrent gcs, both young & old, global (explicit system.gc() invoking a concurrent gobal), and concurrent mode failures (degens) of each kind of collection. So I am guessing at some point we'll need to expand this semantics smoothly to accommodate these other kinds of collection.

However, this can be done later as an RFE that smoothly integrates what JFR et al. do as well.)

ysramakrishna · 2025-07-25T21:17:16Z

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

-               num_regions(),
-               byte_size_in_proper_unit(ShenandoahHeapRegion::region_size_bytes()),
-               proper_unit_for_byte_size(ShenandoahHeapRegion::region_size_bytes()));
+  bool is_generational = mode()->is_generational();


ysramakrishna · 2025-07-25T21:36:58Z

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

+    st->print_cr(" %zu x " PROPERFMT " regions",
+                num_regions(),
+                PROPERFMTARGS(ShenandoahHeapRegion::region_size_bytes()));


I'd print this info for GenShen above as well.

openjdk bot added hotspot-gc hotspot-gc-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Jul 25, 2025

rgithubli marked this pull request as ready for review July 25, 2025 14:08

openjdk bot added the rfr Pull request is ready for review label Jul 25, 2025

8364081: Shenandoah & GenShen logging improvement

1d51fcf

rgithubli force-pushed the 8364081-pr branch from 235aac2 to 1d51fcf Compare July 25, 2025 15:51

earthling-amzn approved these changes Jul 25, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Jul 25, 2025

ysramakrishna reviewed Jul 25, 2025

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