查找JVM端口库的内存使用情况详细信息

Question

这来自正在运行的IBM JVM（1.7）的核心转储。
如何找到用于（185,624,064B）的“端口库”内存是什么？ “未使用”是什么意思？

    0SECTION       NATIVEMEMINFO subcomponent dump routine
NULL           =================================
0MEMUSER
1MEMUSER       JRE: 593,910,528 bytes / 7280 allocations
1MEMUSER       |
2MEMUSER       +--VM: 544,510,528 bytes / 5987 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Classes: 57,037,616 bytes / 1746 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Shared Class Cache: 16,777,312 bytes / 2 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 40,260,304 bytes / 1744 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Memory Manager (GC): 276,343,080 bytes / 794 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Java Heap: 268,439,552 bytes / 1 allocation
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 7,903,528 bytes / 793 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Threads: 22,618,136 bytes / 409 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Java Stack: 1,460,272 bytes / 66 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Native Stack: 20,054,016 bytes / 68 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 1,103,848 bytes / 275 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Trace: 721,064 bytes / 418 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JVMTI: 17,784 bytes / 13 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JNI: 701,192 bytes / 1966 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Port Library: 185,624,064 bytes / 68 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Unused <32bit allocation regions: 185,614,504 bytes / 1 allocation
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 9,560 bytes / 67 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Other: 1,447,592 bytes / 573 allocations
1MEMUSER       |
2MEMUSER       +--JIT: 48,401,712 bytes / 1182 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JIT Code Cache: 18,874,368 bytes / 9 allocations
2MEMUSER       |  |
3MEMUSER       |  +--JIT Data Cache: 12,583,296 bytes / 6 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Other: 16,944,048 bytes / 1167 allocations
1MEMUSER       |
2MEMUSER       +--Class Libraries: 998,288 bytes / 111 allocations
2MEMUSER       |  |
3MEMUSER       |  +--Harmony Class Libraries: 2,000 bytes / 1 allocation
2MEMUSER       |  |
3MEMUSER       |  +--VM Class Libraries: 996,288 bytes / 110 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--sun.misc.Unsafe: 875,440 bytes / 33 allocations
4MEMUSER       |  |  |  |
5MEMUSER       |  |  |  +--Direct Byte Buffers: 463,392 bytes / 28 allocations
4MEMUSER       |  |  |  |
5MEMUSER       |  |  |  +--Other: 412,048 bytes / 5 allocations
3MEMUSER       |  |  |
4MEMUSER       |  |  +--Other: 120,848 bytes / 77 allocations

Answer 1

该内存保留用于某些本机结构（某些与类和线程相关的数据），当使用-Xcompressedrefs时，这些本机结构必须位于底部4GB的内存中。

预留会将可用空间保留在地址空间的底部4GB中，这样它就不会被不需要驻留在其中的其他分配所填满。

可以在最新版本中使用-Xmcrs选项配置保留大小。 请参阅： https : //www-01.ibm.com/support/knowledgecenter/SSYKE2_7.0.0/com.ibm.java.aix.70.doc/diag/appendixes/cmdline/xmcrs.html

我的理解是，该空间在诊断中被标记为未使用，因为只有在子空间分配给特定用途之前，该空间才由RAM支持，然后才会归因于另一部分。 因此，除非需要更多空间，否则可用空间会随着时间而减少，然后将保留一个新的（较小的）块并将其添加到未使用的列表中。