jdk-24/hotspot/test/gc/g1/TestHumongousShrinkHeap.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * 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.
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/**
 * @ignore 8041506, 8041946, 8042051
 * @test TestHumongousShrinkHeap
 * @bug 8036025
 * @summary Verify that heap shrinks after GC in the presence of fragmentation due to humongous objects
 * @library /testlibrary
 * @run main/othervm -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=50 -XX:+UseG1GC -XX:G1HeapRegionSize=1M -verbose:gc TestHumongousShrinkHeap
 */

import java.lang.management.ManagementFactory;
import java.lang.management.MemoryUsage;
import java.util.ArrayList;
import java.util.List;
import sun.management.ManagementFactoryHelper;
import static com.oracle.java.testlibrary.Asserts.*;

public class TestHumongousShrinkHeap {

    public static final String MIN_FREE_RATIO_FLAG_NAME = "MinHeapFreeRatio";
    public static final String MAX_FREE_RATIO_FLAG_NAME = "MaxHeapFreeRatio";

    private static final ArrayList<ArrayList<byte[]>> garbage = new ArrayList<>();
    private static final int PAGE_SIZE = 1024 * 1024; // 1M
    private static final int PAGES_NUM = 5;


    public static void main(String[] args) {
        new TestHumongousShrinkHeap().test();
    }

    private final void test() {
        System.gc();
        MemoryUsagePrinter.printMemoryUsage("init");

        eat();
        MemoryUsagePrinter.printMemoryUsage("eaten");
        MemoryUsage muFull = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();

        free();
        MemoryUsagePrinter.printMemoryUsage("free");
        MemoryUsage muFree = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();

        assertLessThan(muFree.getCommitted(), muFull.getCommitted(), String.format(
                "committed free heap size is not less than committed full heap size, heap hasn't been shrunk?%n"
                + "%s = %s%n%s = %s",
                MIN_FREE_RATIO_FLAG_NAME,
                ManagementFactoryHelper.getDiagnosticMXBean().getVMOption(MIN_FREE_RATIO_FLAG_NAME).getValue(),
                MAX_FREE_RATIO_FLAG_NAME,
                ManagementFactoryHelper.getDiagnosticMXBean().getVMOption(MAX_FREE_RATIO_FLAG_NAME).getValue()
        ));
    }

    private void eat() {
        int HumongousObjectSize = Math.round(.9f * PAGE_SIZE);
        System.out.println("Will allocate objects of size=" +
                MemoryUsagePrinter.humanReadableByteCount(HumongousObjectSize, true));

        for (int i = 0; i < PAGES_NUM; i++) {
            ArrayList<byte[]> stuff = new ArrayList<>();
            eatList(stuff, 100, HumongousObjectSize);
            MemoryUsagePrinter.printMemoryUsage("eat #" + i);
            garbage.add(stuff);
        }
    }

    private void free() {
        // do not free last one list
        garbage.subList(0, garbage.size() - 1).clear();

        // do not free last one element from last list
        ArrayList stuff = garbage.get(garbage.size() - 1);
        stuff.subList(0, stuff.size() - 1).clear();
        System.gc();
    }

    private static void eatList(List garbage, int count, int size) {
        for (int i = 0; i < count; i++) {
            garbage.add(new byte[size]);
        }
    }
}

/**
 * Prints memory usage to standard output
 */
class MemoryUsagePrinter {

    public static String humanReadableByteCount(long bytes, boolean si) {
        int unit = si ? 1000 : 1024;
        if (bytes < unit) {
            return bytes + " B";
        }
        int exp = (int) (Math.log(bytes) / Math.log(unit));
        String pre = (si ? "kMGTPE" : "KMGTPE").charAt(exp - 1) + (si ? "" : "i");
        return String.format("%.1f %sB", bytes / Math.pow(unit, exp), pre);
    }

    public static void printMemoryUsage(String label) {
        MemoryUsage memusage = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
        float freeratio = 1f - (float) memusage.getUsed() / memusage.getCommitted();
        System.out.format("[%-24s] init: %-7s, used: %-7s, comm: %-7s, freeRatio ~= %.1f%%%n",
                label,
                humanReadableByteCount(memusage.getInit(), true),
                humanReadableByteCount(memusage.getUsed(), true),
                humanReadableByteCount(memusage.getCommitted(), true),
                freeratio * 100
        );
    }
}