8272364: Parallel GC adaptive size policy may shrink the heap below MinHeapSize

Reviewed-by: ayang, rkennke

src/hotspot/share/gc/shared/genArguments.cpp

@@ -264,6 +264,9 @@ void GenArguments::initialize_size_info() {
       // size can be too small.
       initial_young_size =
         clamp(scale_by_NewRatio_aligned(InitialHeapSize, GenAlignment), NewSize, max_young_size);
+
+      // Derive MinNewSize from MinHeapSize
+      MinNewSize = MIN2(scale_by_NewRatio_aligned(MinHeapSize, GenAlignment), initial_young_size);
     }
   }
 

test/hotspot/jtreg/gc/arguments/TestParallelGCErgo.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package gc.arguments;
+
+/*
+ * @test TestParallelGCErgo
+ * @bug 8272364
+ * @requires vm.gc.Parallel
+ * @summary Verify ParallelGC minimum young and old ergonomics are setup correctly
+ * @modules java.base/jdk.internal.misc
+ * @library /test/lib
+ * @library /
+ * @run driver gc.arguments.TestParallelGCErgo
+ */
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.Platform;
+
+public class TestParallelGCErgo {
+    private static final long HEAPWORD_SIZE = Platform.is64bit() ? 8 : 4;
+    // Must be a power of 2
+    private static final long GEN_ALIGNMENT = 64 * 1024 * HEAPWORD_SIZE;
+
+    private static final long MINIMUM_HEAP_SIZE = 256 * 1024 * 1024; // 256M
+    private static final long EXPECTED_MIN_YOUNG = alignDown(MINIMUM_HEAP_SIZE / 3, GEN_ALIGNMENT);
+    private static final long EXPECTED_MIN_OLD = MINIMUM_HEAP_SIZE - EXPECTED_MIN_YOUNG;  // heap size = young size + old size
+
+    // s has to be a power of 2
+    private static long alignDown(long s, long align) {
+        return s & (~(align-1));
+    }
+
+    public static void main(String[] args) throws Exception {
+        ArrayList<String> flagList = new ArrayList<String>();
+        flagList.add("-XX:+UseParallelGC");
+        flagList.add("-Xms256m");
+        flagList.add("-Xmx1g");
+        flagList.add("-Xlog:gc+heap=trace");
+        flagList.add("-version");
+
+        OutputAnalyzer output = GCArguments.executeTestJava(flagList);
+        output.shouldHaveExitValue(0);
+
+        String stdout = output.getStdout();
+        long minimumHeap = getFlagValue("Minimum heap", stdout);
+        if (minimumHeap != MINIMUM_HEAP_SIZE) {
+            throw new RuntimeException("Wrong value for minimum heap. Expected " + MINIMUM_HEAP_SIZE + " but got " + minimumHeap);
+        }
+
+        long minimumYoung = getFlagValue("Minimum young", stdout);
+        if (minimumYoung != EXPECTED_MIN_YOUNG) {
+            throw new RuntimeException("Wrong value for minimum young. Expected " + EXPECTED_MIN_YOUNG + " but got " + minimumYoung);
+        }
+
+        long minimumOld = getFlagValue("Minimum old", stdout);
+        if (minimumOld != EXPECTED_MIN_OLD) {
+            throw new RuntimeException("Wrong value for minimum old. Expected " + EXPECTED_MIN_OLD + " but got " + minimumOld);
+        }
+    }
+
+    private static long getFlagValue(String flag, String where) {
+        Matcher m = Pattern.compile(flag + " \\d+").matcher(where);
+        if (!m.find()) {
+            throw new RuntimeException("Could not find value for flag " + flag + " in output string");
+        }
+        String match = m.group();
+        return Long.parseLong(match.substring(match.lastIndexOf(" ") + 1, match.length()));
+    }
+
+}