Java Memory Structure

Java Memory Structure

• 1.
  Haim Yadid JVM MemoryStructure
• 2.
  About Me • Developingsoftware since 1984 • Basic -> Pascal -> C -> C++ -> Java -> Kotlin • Developer , architect, group manager • Independent performance expert for 8 years • Group manager in • Java.IL
• 3.
  • Founded inthe Beginning of 2016 • Disrupt the small businesses insurance field • Providing online experience which is simple, fast and transparent • HQ@Palo Alto / RnD@Kfar Saba (Israel) / Austin-TX • We started to write real code on May 2016
• 4.
  Heap • -Xms • -Xmx XmsXmx Max Init
• 5.
  Physical vs ProcessMemory 0 2^32/2^48Process Address Space Physical memory0 Page Swap Page Page Page Reserved/Virtual Page Page Page Page Committed - activeCommitted - inactive
• 6.
  Heap structure • JMX:java.lang.Memory::HeapMemoryUsage • Continuous address space Used VirtualCommited Max Init
• 7.
  JVisualVM Heap
• 8.
  Not Only Heap •Heap • Code cache • Meta spaces (Native) • Native memory Heap Code Cache 0 2^32/2^48 Native Native Native Meta Meta
• 9.
  Meta Space • Classesbyte code • Part of native memory. • Need not be continuous in memory or pre reserved. • Limit by -XX:MaxMetaspaceSize=
• 10.
  JVisualVM JMX : java.lang.MemoryPool.Metaspace::usage
• 11.
  Code cache • JIT’edhotspot methods (machine code) • -XX:InitialCodeCacheSize=2555904 (2.5MB) • -XX:ReservedCodeCacheSize=251658240 (240MB) • codecache flushing -XX:+UseCodeCacheFlushing
• 12.
  JVisualVM JMX : java.lang.MemoryPool.CodeCache::usage
• 13.
  Native Memory • Threadstacks (1MB for 64 bit OS) • Native allocations • Direct byte buffer java.nio.DirectByteBuffer • Limit by : -XX:MaxDirectMemorySize= • unsafe.allocateMemory • JNI malloc()
• 14.
  Calculating it All •Heap Max = 1 GB • 100 threads = 100 MB • Code cache 256 MB • Meta space 100 MB
• 15.
  Native Memory Tracking java-XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary -XX:+PrintNMTStatistics
• 16.
  jcmd <pid> VM.native_memorysummary Native Memory Tracking: Total: reserved=5808103KB, committed=1987515KB - Java Heap (reserved=4194304KB, committed=1647104KB) (mmap: reserved=4194304KB, committed=1647104KB) - Class (reserved=1118666KB, committed=77258KB) (classes #12468) (malloc=10698KB #17369) (mmap: reserved=1107968KB, committed=66560KB) - Thread (reserved=44541KB, committed=44541KB) (thread #45) (stack: reserved=44192KB, committed=44192KB) (malloc=137KB #230) (arena=212KB #89) ….. -
• 17.
  Docker -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=
• 18.
  Lorem Ipsum Dolor Questions?