对象内存直接在老年代分配

编程语言 2018-04-26 13:02:16 阅读次数: 5

对象优先在新生代分配，但是有的情况对象直接在老年代分配，如下：

1、分配的对象大小大于eden space。适合所有收集器。

2、eden space剩余空间不足分配，且需要分配对象内存大小不小于eden space总空间的一半，直接分配到老年代，不触发Minor GC。适合-XX:+UseParallelGC、-XX:+UseParallelOldGC，即适合Parallel Scavenge。

3、大对象直接进入老年代，使用-XX:PretenureSizeThreshold参数控制，适合-XX:+UseSerialGC、-XX:+UseParNewGC、-XX:+UseConcMarkSweepGC，即适合Serial和ParNew收集器。

以下是测试过程：

一、第一种情况。

测试代码：

	/**
	 * 对象大小超过了eden space大小，-Xms30m -Xmx30m -Xmn10m -XX:+PrintGCDetails
	 */
	private static void testMoreThanEden() {

		/* Eden区为8M，from/to space各为1M */
		LargeObject largeOb1 = new LargeObject(_1M * 8, "largeOb1");
	}

1、测试环境：Java HotSpot(TM) 64-Bit Server VM

-XX:+UseSerialGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

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Over Constructing LargeObject largeOb1

Heap
 def new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f168, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 tenured generation   total 10240K, used 8192K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  80% used [0x00000000ff600000, 0x00000000ffe00010, 0x00000000ffe00200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
2、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParNewGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails
测试结果： 
Over Constructing LargeObject largeOb1

Heap
 par new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f168, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 tenured generation   total 10240K, used 8192K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  80% used [0x00000000ff600000, 0x00000000ffe00010, 0x00000000ffe00200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
Java HotSpot(TM) 64-Bit Server VM warning: Using the ParNew young collector with the Serial old collector is deprecated and will likely be removed in a future release
3、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParallelGC/-XX:+UseParallelOldGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Heap
 PSYoungGen      total 9216K, used 1148K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 14% used [0x00000000ff600000,0x00000000ff71f168,0x00000000ffe00000)
  from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
  to   space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
 ParOldGen       total 10240K, used 8192K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  object space 10240K, 80% used [0x00000000fec00000,0x00000000ff400010,0x00000000ff600000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
4、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseConcMarkSweepGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails
测试结果： 
Over Constructing LargeObject largeOb1

Heap
 par new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f0c8, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 concurrent mark-sweep generation total 10240K, used 8192K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K

二、第二种情况，分三个测试方法代码来测试，只有第一个测试方法测试所有收集器。

测试代码：

	/**
	 * -Xms30m -Xmx30m -Xmn10m -XX:+PrintGCDetails，如果eden
	 * space剩余空间不足分配，且需要分配的大小不小于eden space总空间的一半，直接分配到老年代，不触发Minor
	 * GC。适合-XX:+UseParallelGC、-XX:+UseParallelOldGC。
	 */
	private static void testMoreThanAHalfEden1() {

		/* eden space为8M，from/to space各为1M */
		LargeObject largeOb1 = new LargeObject(_1M * 2, "largeOb1");
		LargeObject largeOb2 = new LargeObject(_1M * 5, "largeOb2");
		largeOb2 = null;

		/* 当largeOb3为1M、2M、3M都会触发Minor GC，从4M开始，直接分配到老年代 */
		LargeObject largeOb3 = new LargeObject(_1M * 4, "largeOb3");
	}

1、测试环境：Java HotSpot(TM) 64-Bit Server VM

-XX:+UseSerialGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

[GC (Allocation Failure) [DefNew: 8152K->554K(9216K), 0.0020207 secs] 8152K->2602K(19456K), 0.0020612 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
Over Constructing LargeObject largeOb3

Heap
 def new generation   total 9216K, used 4892K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  52% used [0x00000000fec00000, 0x00000000ff03cb68, 0x00000000ff400000)
  from space 1024K,  54% used [0x00000000ff500000, 0x00000000ff58a800, 0x00000000ff600000)
  to   space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
 tenured generation   total 10240K, used 2048K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  20% used [0x00000000ff600000, 0x00000000ff800010, 0x00000000ff800200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
2、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParNewGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

[GC (Allocation Failure) [ParNew: 8152K->564K(9216K), 0.0015776 secs] 8152K->2612K(19456K), 0.0016120 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
Over Constructing LargeObject largeOb3

Heap
 par new generation   total 9216K, used 4903K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  52% used [0x00000000fec00000, 0x00000000ff03cb68, 0x00000000ff400000)
  from space 1024K,  55% used [0x00000000ff500000, 0x00000000ff58d1c0, 0x00000000ff600000)
  to   space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
 tenured generation   total 10240K, used 2048K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  20% used [0x00000000ff600000, 0x00000000ff800010, 0x00000000ff800200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
Java HotSpot(TM) 64-Bit Server VM warning: Using the ParNew young collector with the Serial old collector is deprecated and will likely be removed in a future release
3、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParallelGC/-XX:+UseParallelOldGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

Over Constructing LargeObject largeOb3

Heap
 PSYoungGen      total 9216K, used 8192K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 100% used [0x00000000ff600000,0x00000000ffe00000,0x00000000ffe00000)
  from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
  to   space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
 ParOldGen       total 10240K, used 4096K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  object space 10240K, 40% used [0x00000000fec00000,0x00000000ff000010,0x00000000ff600000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
4、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseConcMarkSweepGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

[GC (Allocation Failure) [ParNew: 8152K->573K(9216K), 0.0045070 secs] 8152K->2623K(19456K), 0.0046730 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 
Over Constructing LargeObject largeOb3

Heap
 par new generation   total 9216K, used 4912K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  52% used [0x00000000fec00000, 0x00000000ff03cb70, 0x00000000ff400000)
  from space 1024K,  55% used [0x00000000ff500000, 0x00000000ff58f550, 0x00000000ff600000)
  to   space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
 concurrent mark-sweep generation total 10240K, used 2050K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
 Metaspace       used 2783K, capacity 4486K, committed 4864K, reserved 1056768K
  class space   used 300K, capacity 386K, committed 512K, reserved 1048576K

测试代码：

	/**
	 * -Xms30m -Xmx30m -Xmn10m -XX:+PrintGCDetails space剩余空间不足分配，且需要分配的大小不小于eden
	 * space总空间的一半，直接分配到老年代，不触发Minor GC。适合-XX:+UseParallelGC、-XX:+UseParallelOldGC。
	 */
	private static void testMoreThanAHalfEden2() {

		/* eden space为8M，from/to space各为1M */
		LargeObject largeOb1 = new LargeObject(_1M * 2, "largeOb1");

		LargeObject largeOb2 = new LargeObject(_1M * 2, "largeOb2");
		largeOb2 = null;

		/* 当largeOb2为2M、3M、4M时，largeOb3直接分配到老年代 ，如果为1M时，largeOb3分配到新生代 */
		LargeObject largeOb3 = new LargeObject(_1M * 4, "largeOb3");
	}
测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParallelGC/-XX:+UseParallelOldGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

Over Constructing LargeObject largeOb3

Heap
 PSYoungGen      total 9216K, used 5244K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 64% used [0x00000000ff600000,0x00000000ffb1f188,0x00000000ffe00000)
  from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
  to   space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
 ParOldGen       total 10240K, used 4096K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  object space 10240K, 40% used [0x00000000fec00000,0x00000000ff000010,0x00000000ff600000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K

测试代码：

	/**
	 * -Xms40m -Xmx40m -Xmn20m -XX:+PrintGCDetails space剩余空间不足分配，且需要分配的大小不小于eden
	 * space总空间的一半，直接分配到老年代，不触发Minor GC。适合-XX:+UseParallelGC、-XX:+UseParallelOldGC。
	 */
	private static void testMoreThanAHalfEden3() {

		/* eden space为16M，from/to space各为2M */
		LargeObject largeOb1 = new LargeObject(_1M * 10, "largeOb1");

		/* 如果小于8M，则触发MinorGC，如果大于等于8M，直接分配到老年代 */
		LargeObject largeOb2 = new LargeObject(_1M * 8, "largeOb2");
	}

测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParallelGC/-XX:+UseParallelOldGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Over Constructing LargeObject largeOb2

Heap
 PSYoungGen      total 17920K, used 11776K [0x00000000fec00000, 0x0000000100000000, 0x0000000100000000)
  eden space 15360K, 76% used [0x00000000fec00000,0x00000000ff780380,0x00000000ffb00000)
  from space 2560K, 0% used [0x00000000ffd80000,0x00000000ffd80000,0x0000000100000000)
  to   space 2560K, 0% used [0x00000000ffb00000,0x00000000ffb00000,0x00000000ffd80000)
 ParOldGen       total 20480K, used 8192K [0x00000000fd800000, 0x00000000fec00000, 0x00000000fec00000)
  object space 20480K, 40% used [0x00000000fd800000,0x00000000fe000010,0x00000000fec00000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K

三、第三种情况。

测试代码：

	/**
	 * -XX:PretenureSizeThreshold=2097152 -Xms20m -Xmx20m -Xmn10m
	 * -XX:+PrintGCDetails，适合-XX:+UseSerialGC、-XX:+UseParNewGC、-XX:+UseConcMarkSweepGC
	 */
	private static void testPretenureSizeThreshold() {

		/* eden space为16M，from/to space各为2M，如果为1M，直接分配在了新生代，如果为2M，直接分配在了老年代 */
		LargeObject largeOb1 = new LargeObject(_1M * 2, "largeOb1");
	}

1、测试环境：Java HotSpot(TM) 64-Bit Server VM

-XX:+UseSerialGC -XX:PretenureSizeThreshold=2097152  -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Heap
 def new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f168, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 tenured generation   total 10240K, used 2048K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  20% used [0x00000000ff600000, 0x00000000ff800010, 0x00000000ff800200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
2、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParNewGC  -XX:PretenureSizeThreshold=2097152  -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails
测试结果： 
Over Constructing LargeObject largeOb1

Heap
 par new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f168, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 tenured generation   total 10240K, used 2048K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
   the space 10240K,  20% used [0x00000000ff600000, 0x00000000ff800010, 0x00000000ff800200, 0x0000000100000000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
Java HotSpot(TM) 64-Bit Server VM warning: Using the ParNew young collector with the Serial old collector is deprecated and will likely be removed in a future release
3、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseParallelGC/-XX:+UseParallelOldGC -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Heap
 PSYoungGen      total 9216K, used 3196K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 39% used [0x00000000ff600000,0x00000000ff91f178,0x00000000ffe00000)
  from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
  to   space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
 ParOldGen       total 10240K, used 0K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  object space 10240K, 0% used [0x00000000fec00000,0x00000000fec00000,0x00000000ff600000)
 Metaspace       used 2784K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K
4、测试环境：Java HotSpot(TM) 64-Bit Server VM
-XX:+UseConcMarkSweepGC -XX:PretenureSizeThreshold=2097152 -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails

测试结果：

Over Constructing LargeObject largeOb1

Heap
 par new generation   total 9216K, used 1148K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  eden space 8192K,  14% used [0x00000000fec00000, 0x00000000fed1f0c8, 0x00000000ff400000)
  from space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
  to   space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
 concurrent mark-sweep generation total 10240K, used 2048K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
 Metaspace       used 2786K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 300K, capacity 386K, committed 512K, reserved 1048576K

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