java - 垃圾回收 : how is Eden space (and the other generation sizes) calculated?

Question

我需要帮助了解我如何从 jmap 获得与 GC 相关的数字和 jstat与我传递给 java 的设置有关。我在具有 16GB 内存的服务器上使用以下设置启动应用程序 (solr):

-XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -Xms12144m -Xmx12144m -XX:NewRatio=4 -XX:SurvivorRatio=8 -XX:+UseCompressedOops

jmap 的输出开始:

Concurrent Mark-Sweep GCHeap Configuration:   MinHeapFreeRatio = 40   MaxHeapFreeRatio = 70   MaxHeapSize      = 12733906944 (12144.0MB)   NewSize          = 2686976 (2.5625MB)   MaxNewSize       = 130809856 (124.75MB)   OldSize          = 5439488 (5.1875MB)   NewRatio         = 4   SurvivorRatio    = 8   PermSize         = 21757952 (20.75MB)   MaxPermSize      = 176160768 (168.0MB)

为什么是NewSize , MaxNewSize , OldSize , 和 PermSize都这么小，当MaxHeapSize大吗？不应该NewSize + OldSize = heap size ？总堆大小不应该接近MaxHeapSize吗？ ？为什么是NewSize OldSize 的一半当NewRatio设置为 4？

其余jmap输出如下。它与上面相匹配，并包含一个部分 concurrent mark-sweep generation我也不知道如何解释。

此外，GC 日志表明“所需幸存者大小”为 6.2MB，这也很奇怪，据我了解 -XX:SurvivorRatio=8应该使幸存者空间成为 NewSize 的 1/8 .

最后，我只看到ParNew我的 GC 日志中的消息，据我所知是 Eden 的 GC。

Heap Usage:New Generation (Eden + 1 Survivor Space):   capacity = 117768192 (112.3125MB)   used     = 20402232 (19.45708465576172MB)   free     = 97365960 (92.85541534423828MB)   17.324059793666528% usedEden Space:   capacity = 104726528 (99.875MB)   used     = 16408336 (15.648208618164062MB)   free     = 88318192 (84.22679138183594MB)   15.667793359863893% usedFrom Space:   capacity = 13041664 (12.4375MB)   used     = 3993896 (3.8088760375976562MB)   free     = 9047768 (8.628623962402344MB)   30.624128945508794% usedTo Space:   capacity = 13041664 (12.4375MB)   used     = 0 (0.0MB)   free     = 13041664 (12.4375MB)   0.0% usedconcurrent mark-sweep generation:   capacity = 12603097088 (12019.25MB)   used     = 7903352408 (7537.22420501709MB)   free     = 4699744680 (4482.02579498291MB)   62.70960505037411% usedPerm Generation:   capacity = 45903872 (43.77734375MB)   used     = 27759192 (26.473228454589844MB)   free     = 18144680 (17.304115295410156MB)   60.472441191889% used

Answer 1

Why are NewSize, MaxNewSize, OldSize, and PermSize all so small, when the MaxHeapSize is large?

尺寸只是他们需要的那么大。如果你产生更多的短期垃圾，NewSize 会更大(我不知道 MaxNewSize 是如何设置的，但它通常比我设置的要小)

concurrent mark-sweep generation

capacity = 最大尺寸，used = used，free = capacity - used。

ParNew messages in my GC log, which I understand is the GC for Eden.

正如您所指出的，新空间很小，所以它经常清理，而旧的空间很大，所以它很少清理。