在javacore和heapdump中堆积:在IBM JVM上有20倍的差异

Question

注意到生产服务器(Websphere8.5.5)开始消耗大量内存.

javacore转储中的数字清楚地表明罪魁祸首是一堆杂乱无章的堆:

|  +--Memory Manager (GC): 5,496,900,272 bytes / 3193 allocations
|  |  |
|  |  +--Java Heap: 5,368,770,560 bytes / 1 allocation
|  |  |
|  |  +--Other: 128,129,712 bytes / 3192 allocations  

但与此同时,在MAT中打开的堆转储报告堆的总容量大约为200M(有时高达300M,但从不多).

它到底意味着什么？堆转储是否值得信赖？如果是,是否有办法释放未使用的堆内存？

更新:完整的NATIVEMEM部分,根据要求

1MEMUSER       JRE: 7,211,791,256 bytes / 39196 allocations
1MEMUSER       |
2MEMUSER       +--VM: 6,772,051,048 bytes / 29934 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Classes: 370,339,176 bytes / 10002 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Shared Class Cache: 62,914,560 bytes / 1 allocation
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 307,424,616 bytes / 10001 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Memory Manager (GC): 5,496,900,272 bytes / 3193 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Java Heap: 5,368,770,560 bytes / 1 allocation
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 128,129,712 bytes / 3192 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Threads: 91,710,312 bytes / 3408 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Java Stack: 5,958,456 bytes / 349 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Native Stack: 68,812,800 bytes / 248 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 16,939,056 bytes / 2811 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Trace: 3,415,376 bytes / 1229 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JVMTI: 17,776 bytes / 13 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JNI: 5,821,768 bytes / 9844 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Port Library: 794,750,560 bytes / 401 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Unused <32bit allocation regions: 794,704,552 bytes / 87 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 46,008 bytes / 314 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Other: 9,095,808 bytes / 1844 allocations
1MEMUSER       |
2MEMUSER       +--JIT: 436,874,280 bytes / 8850 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JIT Code Cache: 268,435,456 bytes / 1 allocation
2MEMUSER       |  |
3MEMUSER       |  +--JIT Data Cache: 48,235,968 bytes / 23 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Other: 120,202,856 bytes / 8826 allocations
1MEMUSER       |
2MEMUSER       +--Class Libraries: 2,865,928 bytes / 412 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Harmony Class Libraries: 2,000 bytes / 1 allocation
2MEMUSER       |  |
3MEMUSER       |  +--VM Class Libraries: 2,863,928 bytes / 411 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--sun.misc.Unsafe: 2,635,720 bytes / 307 allocations
4MEMUSER       |  |  |  |
5MEMUSER       |  |  |  +--Direct Byte Buffers: 2,625,112 bytes / 304 allocations
4MEMUSER       |  |  |  |
5MEMUSER       |  |  |  +--Other: 10,608 bytes / 3 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 228,208 bytes / 104 allocations

Answer 1

该NATIVEMEMINFO部分显示了虚拟内存,因此5,368,770,560只是意味着JVM实际上为堆分配了大量内存.实际驻留多少取决于实际堆大小和堆使用情况.例如,如果在终身地区积累了大量垃圾,然后在完整的GC中进行清理,那么可能在某些时候这些页面成为常驻,但实际生活多少取决于许多因素.我相信当JVM启动时,它实际上分配了完整的大小,-Xmx所以我认为你总是会在NATIVEMEMINFO中看到堆的完整大小(它也可能只是它分配-Xms,所以如果你看到的大于-Xms,然后它意味着压力驱使堆增加[虽然当然,注意正常的锯齿 ]).

在MAT中加载转储时,它会运行完整的垃圾收集,并默认从主视图中删除任何无法访问的对象.您可以单击Overview页面上的"Unreachable Objects Histogram"链接,并滚动到底部的浅堆总计行的总和,以查看heapdump中有多少"trash".MAT首选项中还有一个选项是"保持无法访问的对象",这会将所有这些对象保留在主MAT视图中,但这通常不是很有用.

所以基本的答案是MAT只显示活动对象,所以在转储时,有200-300MB的活动对象.剩下的可能是垃圾,或者根本就没有,NATIVEMEMINFO只是显示虚拟大小.

查看堆使用情况的更好方法是在GCMV中使用verbosegc和load :

-Xverbosegclog:verbosegc.%seq.log,20,50000