| /* |
| * Copyright (c) 2014, 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. |
| */ |
| |
| import java.lang.management.MemoryPoolMXBean; |
| import java.util.Optional; |
| |
| import sun.hotspot.WhiteBox; |
| |
| /** |
| * Helper class aimed to provide information about alignment of objects in |
| * particular heap space, expected memory usage after objects' allocation so on. |
| */ |
| public class AlignmentHelper { |
| private static final WhiteBox WHITE_BOX = WhiteBox.getWhiteBox(); |
| |
| private static final long OBJECT_ALIGNMENT_IN_BYTES_FOR_32_VM = 8L; |
| |
| /** |
| * Max relative allowed actual memory usage deviation from expected memory |
| * usage. |
| */ |
| private static final float MAX_RELATIVE_DEVIATION = 0.05f; // 5% |
| |
| public static final long OBJECT_ALIGNMENT_IN_BYTES = Optional.ofNullable( |
| AlignmentHelper.WHITE_BOX.getIntxVMFlag("ObjectAlignmentInBytes")) |
| .orElse(AlignmentHelper.OBJECT_ALIGNMENT_IN_BYTES_FOR_32_VM); |
| |
| public static final long SURVIVOR_ALIGNMENT_IN_BYTES = Optional.ofNullable( |
| AlignmentHelper.WHITE_BOX.getIntxVMFlag("SurvivorAlignmentInBytes")) |
| .orElseThrow(() ->new AssertionError( |
| "Unable to get SurvivorAlignmentInBytes value")); |
| /** |
| * Min amount of memory that will be occupied by an object. |
| */ |
| public static final long MIN_OBJECT_SIZE |
| = AlignmentHelper.WHITE_BOX.getObjectSize(new Object()); |
| /** |
| * Min amount of memory that will be occupied by an empty byte array. |
| */ |
| public static final long MIN_ARRAY_SIZE |
| = AlignmentHelper.WHITE_BOX.getObjectSize(new byte[0]); |
| |
| /** |
| * Precision at which actual memory usage in a heap space represented by |
| * this sizing helper could be measured. |
| */ |
| private final long memoryUsageMeasurementPrecision; |
| /** |
| * Min amount of memory that will be occupied by an object allocated in a |
| * heap space represented by this sizing helper. |
| */ |
| private final long minObjectSizeInThisSpace; |
| /** |
| * Object's alignment in a heap space represented by this sizing helper. |
| */ |
| private final long objectAlignmentInThisRegion; |
| /** |
| * MemoryPoolMXBean associated with a heap space represented by this sizing |
| * helper. |
| */ |
| private final MemoryPoolMXBean poolMXBean; |
| |
| private static long alignUp(long value, long alignment) { |
| return ((value - 1) / alignment + 1) * alignment; |
| } |
| |
| protected AlignmentHelper(long memoryUsageMeasurementPrecision, |
| long objectAlignmentInThisRegion, long minObjectSizeInThisSpace, |
| MemoryPoolMXBean poolMXBean) { |
| this.memoryUsageMeasurementPrecision = memoryUsageMeasurementPrecision; |
| this.minObjectSizeInThisSpace = minObjectSizeInThisSpace; |
| this.objectAlignmentInThisRegion = objectAlignmentInThisRegion; |
| this.poolMXBean = poolMXBean; |
| } |
| |
| /** |
| * Returns how many objects have to be allocated to fill |
| * {@code memoryToFill} bytes in this heap space using objects of size |
| * {@code objectSize}. |
| */ |
| public int getObjectsCount(long memoryToFill, long objectSize) { |
| return (int) (memoryToFill / getObjectSizeInThisSpace(objectSize)); |
| } |
| |
| /** |
| * Returns amount of memory that {@code objectsCount} of objects with size |
| * {@code objectSize} will occupy this this space after allocation. |
| */ |
| public long getExpectedMemoryUsage(long objectSize, int objectsCount) { |
| long correctedObjectSize = getObjectSizeInThisSpace(objectSize); |
| return AlignmentHelper.alignUp(correctedObjectSize * objectsCount, |
| memoryUsageMeasurementPrecision); |
| } |
| |
| /** |
| * Returns current memory usage in this heap space. |
| */ |
| public long getActualMemoryUsage() { |
| return poolMXBean.getUsage().getUsed(); |
| } |
| |
| /** |
| * Returns maximum memory usage deviation from {@code expectedMemoryUsage} |
| * given the max allowed relative deviation equal to |
| * {@code relativeDeviation}. |
| * |
| * Note that value returned by this method is aligned according to |
| * memory measurement precision for this heap space. |
| */ |
| public long getAllowedMemoryUsageDeviation(long expectedMemoryUsage) { |
| long unalignedDeviation = (long) (expectedMemoryUsage * |
| AlignmentHelper.MAX_RELATIVE_DEVIATION); |
| return AlignmentHelper.alignUp(unalignedDeviation, |
| memoryUsageMeasurementPrecision); |
| } |
| |
| /** |
| * Returns amount of memory that will be occupied by an object with size |
| * {@code objectSize} in this heap space. |
| */ |
| public long getObjectSizeInThisSpace(long objectSize) { |
| objectSize = Math.max(objectSize, minObjectSizeInThisSpace); |
| |
| long alignedObjectSize = AlignmentHelper.alignUp(objectSize, |
| objectAlignmentInThisRegion); |
| long sizeDiff = alignedObjectSize - objectSize; |
| |
| // If there is not enough space to fit padding object, then object will |
| // be aligned to {@code 2 * objectAlignmentInThisRegion}. |
| if (sizeDiff >= AlignmentHelper.OBJECT_ALIGNMENT_IN_BYTES |
| && sizeDiff < AlignmentHelper.MIN_OBJECT_SIZE) { |
| alignedObjectSize += AlignmentHelper.MIN_OBJECT_SIZE; |
| alignedObjectSize = AlignmentHelper.alignUp(alignedObjectSize, |
| objectAlignmentInThisRegion); |
| } |
| |
| return alignedObjectSize; |
| } |
| @Override |
| public String toString() { |
| StringBuilder builder = new StringBuilder(); |
| |
| builder.append(String.format("AlignmentHelper for memory pool '%s':%n", |
| poolMXBean.getName())); |
| builder.append(String.format("Memory usage measurement precision: %d%n", |
| memoryUsageMeasurementPrecision)); |
| builder.append(String.format("Min object size in this space: %d%n", |
| minObjectSizeInThisSpace)); |
| builder.append(String.format("Object alignment in this space: %d%n", |
| objectAlignmentInThisRegion)); |
| |
| return builder.toString(); |
| } |
| } |