G1 GC分配的内存大于堆大小。

Question

我为应用服务器更改GC。现在我使用G1 GC。我有30 GB内存。对于初始测试，我只将Xms和Xmx值设置为相同的23040 mb。

我使用的设置：

 -Xms23040m -Xmx23040m  -XX:+UseG1GC -XX:MetaspaceSize=512M -XX:MaxMetaspaceSize=1536m 

如果我使用GCEasy GC，我有有趣的G1度量。

   Generation         | Allocated | Peak
   Young Gen          | 13.38     | 3.37
   Old Gen            | 21.17     | 485mb
   Meta Space         | 1.5       | n/a
   Young + old + Meta | 23.78     | 13.61

总计是36.05 GB的怎么回事？GCEasy图林克在这里。

我不明白为什么分配的内存大于最大堆大小？

GC初始日志：

OpenJDK 64-Bit Server VM (25.282-b08) for linux-amd64 JRE (1.8.0_282-b08), built on Jan 20 2021 11:56:52 by "jenkins" with gcc 7.5.0
Memory: 4k page, physical 31389860k(23816948k free), swap 0k(0k free)
CommandLine flags: -XX:GCLogFileSize=3145728 -XX:InitialHeapSize=23923261440 -XX:MaxHeapSize=23923261440 -XX:MaxMetaspaceSize=1610612736 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:-TraceClassUnloading -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC -XX:+UseGCLogFileRotation

GC暂停日志：

    2022-01-19T08:18:40.340-0500: 45739.624: [GC pause (G1 Evacuation Pause) (young), 0.0675291 secs]
   [Parallel Time: 42.0 ms, GC Workers: 1]
      [GC Worker Start (ms):  45739624.2]
      [Ext Root Scanning (ms):  10.8]
      [Update RS (ms):  5.1]
         [Processed Buffers:  76]
      [Scan RS (ms):  2.1]
      [Code Root Scanning (ms):  2.9]
      [Object Copy (ms):  21.0]
      [Termination (ms):  0.0]
         [Termination Attempts:  1]
      [GC Worker Other (ms):  0.0]
      [GC Worker Total (ms):  41.9]
      [GC Worker End (ms):  45739666.1]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 5.8 ms]
   [Other: 19.7 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 16.8 ms]
      [Ref Enq: 0.1 ms]
      [Redirty Cards: 0.1 ms]
      [Humongous Register: 0.1 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 2.3 ms]
   [Eden: 13632.0M(13632.0M)->0.0B(13632.0M) Survivors: 57344.0K->57344.0K Heap: 13933.2M(22816.0M)->307.2M(22816.0M)]
 [Times: user=0.07 sys=0.00, real=0.07 secs] 

这是否意味着GCEasy.io有错误来显示正确的度量标准？当我使用并行GC时，没有类似的问题。(分配的内存是，而不是，大于Xmx)

Answer 1

该表中列出的分配大小包括梅斯帕斯。Metaspace是与java对象堆分离的内存池。因此，堆和元空间的总和可以超过最大堆大小。

->0.0B(13632.0M)幸存者: 57344.0K->57344.0K堆: 13933.2M(22816.0M)->307.2M(22816.0M)

这表明总的堆大小(所有代)为22 at，在最大堆限制内。也许gceasy把堆的总大小误认为是老一代？