Java保留内存高于G1 GC /GC驻留内存

Question

java进程使用G1GC使用的驻留内存比XMX和NMT报告的内存要高得多。

java -version
openjdk version "11.0.6" 2020-01-14 LTS
OpenJDK Runtime Environment 18.9 (build 11.0.6+10-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.6+10-LTS, mixed mode, sharing)

top output
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
    787 root      20   0   99.9g  85.4g  22120 S  1053 66.8  11904:11 java

JVM Arguments
/usr/bin/java -Xms75g -Xmx75g -XX:NativeMemoryTracking=summary -XX:MaxGCPauseMillis=50 
-XX:G1RSetSparseRegionEntries=4096 -XX:G1HeapRegionSize=32M 
-Xlog:gc*=info,gc+phases=debug:file=/var/log/gc.log:time,uptimemillis,level,tags:filecount=5,filesize=50M  -XX:+UseG1GC

Native Memory Tracking:

Total: reserved=81376MB, committed=80879MB
-                 Java Heap (reserved=76800MB, committed=76800MB)
                            (mmap: reserved=76800MB, committed=76800MB)

-                     Class (reserved=65MB, committed=65MB)
                            (classes #9993)
                            (  instance classes #9216, array classes #777)
                            (malloc=1MB #29050)
                            (mmap: reserved=64MB, committed=63MB)
                            (  Metadata:   )
                            (    reserved=64MB, committed=63MB)
                            (    used=62MB)
                            (    free=1MB)
                            (    waste=0MB =0.00%)

-                    Thread (reserved=348MB, committed=35MB)
                            (thread #345)
                            (stack: reserved=346MB, committed=33MB)
                            (malloc=1MB #2072)
                            (arena=1MB #688)

-                      Code (reserved=244MB, committed=62MB)
                            (malloc=2MB #6831)
                            (mmap: reserved=242MB, committed=59MB)

-                        GC (reserved=3239MB, committed=3239MB)
                            (malloc=356MB #58172)
                            (mmap: reserved=2883MB, committed=2883MB)

-                  Compiler (reserved=2MB, committed=2MB)
                            (malloc=3MB #2963)

-                  Internal (reserved=16MB, committed=16MB)
                            (malloc=16MB #8415)

-                     Other (reserved=643MB, committed=643MB)
                            (malloc=643MB #296)

-                    Symbol (reserved=12MB, committed=12MB)
                            (malloc=10MB #122802)
                            (arena=3MB #1)

-    Native Memory Tracking (reserved=4MB, committed=4MB)
                            (tracking overhead=4MB)

NMT报告了大约80 is的内存使用情况，但是java进程的驻留内存超过85 is。随着时间的推移，两者之间的差距不断扩大。对于运行相同应用程序的另一个VM，驻留内存超过95 VM，而NMT内存再次只有82 VM。由于这种不断增长的内存消耗，这个应用程序最终被操作系统杀手杀死了。

是什么导致了两者之间的差异？如何减少这个应用程序的内存足迹呢？

Answer 1

“本发行版中的NMT不跟踪第三方本机代码内存分配和JDK类库。”https://docs.oracle.com/javase/8/docs/technotes/guides/vm/nmt-8.html。

基本上，您可以通过JNI访问第三方本机代码，以及在JVM之外显式分配存储的ByteBuffers之类的东西。