jdk-24/hotspot/test/gc/TestSmallHeap.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * 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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/**
 * @test TestSmallHeap
 * @bug 8067438
 * @requires vm.gc=="null"
 * @requires (vm.opt.AggressiveOpts=="null") | (vm.opt.AggressiveOpts=="false")
 * @requires vm.compMode != "Xcomp"
 * @requires vm.opt.UseCompressedOops != false
 * @summary Verify that starting the VM with a small heap works
 * @library /testlibrary /test/lib
 * @modules java.management/sun.management
 * @build TestSmallHeap
 * @run main ClassFileInstaller sun.hotspot.WhiteBox
 * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -Xmx2m -XX:+UseParallelGC TestSmallHeap
 * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -Xmx2m -XX:+UseSerialGC TestSmallHeap
 * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -Xmx2m -XX:+UseG1GC TestSmallHeap
 * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -Xmx2m -XX:+UseConcMarkSweepGC TestSmallHeap
 */

/* Note: It would be nice to verify the minimal supported heap size (2m) here,
 * but we align the heap size based on the card table size. And the card table
 * size is aligned based on the minimal pages size provided by the os. This
 * means that on most platforms, where the minimal page size is 4k, we get a
 * minimal heap size of 2m but on Solaris/Sparc we have a page size of 8k and
 * get a minimal heap size of 4m. And on platforms where the page size is 64k
 * we get a minimal heap size of 32m. We never use large pages for the card table.
 *
 * There is also no check in the VM for verifying that the maximum heap size
 * is larger than the supported minimal heap size. This means that specifying
 * -Xmx1m on the command line is fine but will give a heap of 2m (or 4m or 32m).
 *
 * To work around these rather strange behaviors this test uses -Xmx2m but then
 * calculates what the expected heap size should be. The calculation is a
 * simplified version of the code in the VM. We assume that the card table will
 * use one page. Each byte in the card table corresponds to 512 bytes on the heap.
 * So, the expected heap size is page_size * 512.
 */

import jdk.test.lib.*;
import com.sun.management.HotSpotDiagnosticMXBean;
import java.lang.management.ManagementFactory;
import static jdk.test.lib.Asserts.*;

import sun.hotspot.WhiteBox;

public class TestSmallHeap {

    public static void main(String[] args) {
        WhiteBox wb = WhiteBox.getWhiteBox();
        int pageSize = wb.getVMPageSize();
        int heapBytesPerCard = 512;
        long expectedMaxHeap = pageSize * heapBytesPerCard;
        String maxHeap
            = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class)
                .getVMOption("MaxHeapSize").getValue();
        assertEQ(Long.parseLong(maxHeap), expectedMaxHeap);
    }
}