On Wed, 3 Dec 2025 19:11:14 GMT, Maurizio Cimadamore <[email protected]>
wrote:
> One more interesting experiment could be to try to enable end position in all
> trees, then run the JDK build and compare with mainline, to see what the
> memory usage looks like (maybe enabling -verbose:gc and looking where it
> peaks).
I attempted this experiment. I ran configure with `--disable-javac-server` and
added `-verbose:gc` to the javac args with the change below. Then I made
trivial edits to `src/java.base/share/classes/java/lang/String.java` and
rebuilt.
With this PR the output was something like
Compiling up to 3385 files for java.base
[0.003s][info][gc] Using G1
[0.239s][info][gc] GC(0) Pause Young (Normal) (G1 Evacuation Pause)
34M->4M(64M) 2.704ms
[0.415s][info][gc] GC(1) Pause Young (Normal) (G1 Evacuation Pause)
31M->10M(64M) 4.419ms
[0.531s][info][gc] GC(2) Pause Young (Normal) (G1 Evacuation Pause)
37M->16M(64M) 4.672ms
[0.568s][info][gc] GC(3) Pause Young (Concurrent Start) (Metadata GC Threshold)
24M->18M(64M) 2.825ms
[0.568s][info][gc] GC(4) Concurrent Mark Cycle
[0.573s][info][gc] GC(4) Pause Remark 19M->19M(64M) 1.349ms
[0.575s][info][gc] GC(4) Pause Cleanup 19M->19M(64M) 0.007ms
[0.575s][info][gc] GC(4) Concurrent Mark Cycle 6.227ms
And without these changes, it looks like it peaked at 36M instead of 37M
[info][gc] GC(2) Pause Young (Normal) (G1 Evacuation Pause) 36M->16M(64M)
---
diff --git a/make/common/JavaCompilation.gmk b/make/common/JavaCompilation.gmk
index 33f5d10535a..e9a800bce5a 100644
--- a/make/common/JavaCompilation.gmk
+++ b/make/common/JavaCompilation.gmk
@@ -254,7 +254,7 @@ define SetupJavaCompilationBody
javacserver.Main --conf=$$($1_JAVAC_SERVER_CONFIG)
else
# No javac server
- $1_JAVAC := $$(INTERIM_LANGTOOLS_ARGS) -m
jdk.compiler.interim/com.sun.tools.javac.Main
+ $1_JAVAC := -verbose:gc $$(INTERIM_LANGTOOLS_ARGS) -m
jdk.compiler.interim/com.sun.tools.javac.Main
ifeq ($$($1_SMALL_JAVA), true)
$1_JAVAC_CMD := $$(JAVA_SMALL) $$($1_JAVA_FLAGS) $$($1_JAVAC)
-------------
PR Comment: https://git.openjdk.org/jdk/pull/28610#issuecomment-3612431977
