MMap - OS Memory Region#
内存分区#
关于 JVM 内存分区,可见我之前写的文章:
Linux 进程内存分区概念。如还未了解,可见:进程的内存 - 《Mark’s DevOps 雜碎》
Java 内存分区,以及它 Linux 进程内存分区的映射关系。如还未了解,可见:把大象装入货柜里——Java容器内存拆解
分阶段占用内存#
实验#
以下结合示例代码 SafepointGDB.java ,以及本书实验环境一节 用 VSCode gdb 去 debug JVM 的环境,来理论结合实验 fact check 分析一下。
bash -c 'echo pid=$$ && read && exec setarch $(uname -m) --addr-no-randomize /home/labile/opensource/jdk/build/linux-x86_64-server-slowdebug-hsdis/jdk/bin/java -XX:NativeMemoryTracking=detail -XX:+PrintNMTStatistics -XX:+AlwaysPreTouch -Xms100m -Xmx100m -server -XX:+UseSerialGC -XX:-UseCompressedOops -XX:+UnlockDiagnosticVMOptions -cp /home/labile/pub-diy/jvm-insider-book/memory/java-obj-layout/out/production/java-obj-layout com.mygraphql.jvm.insider.safepoint.SafepointGDB'
不难看出,每个内存 Region 的使用,分为几个阶段:
Reserved Region. 调用 mmap syscall,保留一大段连续的地址空间(未在 kernel 中占用 RSS 内存),内存页不能读写。对应 mmap 权限 PROT_NONE
Commit Region. 在真正需要使用一个内存块之前,调用 mmap syscall,对
Reserved Region
的一大段连续的地址空间中的 一部分(或全部)连接内存页,设置可以读写或执行的权限(但还是未在 kernel 中占用 RSS 内存)。对应 mmap 权限 PROT_READ|PROT_WRITE|PROT_EXEC 。Read/Write(touch) memory. 程序首次读写内存页时,在 kernel 中计入 RSS 内存。
看到 Reserved/Commit 这些术语,大概就知道平时我们监控 Java 内存使用时,Reserved Memory/Commit Memory 是什么玩意了。
上图同时描述了 Native Memory Tracking 实现的数据结构。 jcmd
的 Native Memory Tracking 相关子命令:
jcmd <pid> VM.native_memory [summary | detail | baseline | summary.diff | detail.diff | shutdown] [scale= KB | MB | GB]
的实现数据就是来源于这个数据结构。
观察#
pmap Linux command#
jcmd System.map#
The jcmd Command - OpenJDK23 - docs.oracle.com
Synopsis
jcmd
[pid | main-class] command… |PerfCounter.print
|-f
filename
jcmd
[-l
]jcmd` `-hCommands for jcmd
System.map
[options] (Linux only)Prints an annotated process memory map of the VM process.
Impact: Low
Note:
The following options must be specified using either key or key
=
value syntax.options:
-H
: (Optional) Human readable format (BOOLEAN, false)
/home/labile/opensource/jdk/build/linux-x86_64-server-slowdebug-hsdis/jdk/bin/jcmd 168171 System.map
Java 退出时打印 mmap: -XX:+PrintMemoryMapAtExit#
Java options: -XX:+PrintMemoryMapAtExit
. Print an annotated memory map at exit.
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintMemoryMapAtExit -XX:NativeMemoryTracking=summary ReadMappedFile
from to vsize prot rss hugetlb pgsz notes info file
========================================================================================================================================================================
0x0000000689400000-0x00000006a0c00000 394264576 rw-p 17076224 0 4K com JAVAHEAP -
0x00000006a0c00000-0x00000007ffc00000 5888802816 ---p 0 0 4K - JAVAHEAP -
0x00000007ffc00000-0x00000007ffd21000 1183744 rw-p 1183744 0 4K com JAVAHEAP /big/jdks/jdk24/lib/server/classes.jsa
0x00000007ffd21000-0x0000000800000000 3010560 rw-p 0 0 4K com JAVAHEAP -
0x00007f0000000000-0x00007f0000d90000 14221312 rw-p 14098432 0 4K com CDS /big/jdks/jdk24/lib/server/classes.jsa
0x00007f0000d90000-0x00007f0001000000 2555904 ---p 0 0 4K - CDS -
0x00007f0001000000-0x00007f0001010000 65536 rw-p 28672 0 4K com CLASS -
0x00007f0001010000-0x00007f0001040000 196608 ---p 0 0 4K - CLASS -
0x00007f0001040000-0x00007f0001050000 65536 rw-p 36864 0 4K com CLASS -
0x00007f0001050000-0x00007f0041000000 1073414144 ---p 0 0 4K - CLASS -
0x0000b49b739f0000-0x0000b49b739f1000 4096 r-xp 4096 0 4K com - /big/jdks/jdk24/bin/java
0x0000b49b73a01000-0x0000b49b73a02000 4096 r--p 4096 0 4K com - /big/jdks/jdk24/bin/java
0x0000b49b73a02000-0x0000b49b73a03000 4096 rw-p 4096 0 4K com - /big/jdks/jdk24/bin/java
0x0000b49ba384e000-0x0000b49ba3881000 208896 rw-p 159744 0 4K com - [heap]
...
0x0000ec2570000000-0x0000ec25700b0000 720896 rw-p 712704 0 4K com META -
0x0000ec25700b0000-0x0000ec2570400000 3473408 ---p 0 0 4K - META -
...
0x0000ec2580fbf000-0x0000ec2580fcf000 65536 ---p 0 0 4K com - -
0x0000ec2580fcf000-0x0000ec25811cd000 2088960 rw-p 12288 0 4K com STACK-1696938-GC-Thread -
0x0000ec25811cd000-0x0000ec25811dd000 65536 ---p 0 0 4K com - -
0x0000ec25811dd000-0x0000ec25813db000 2088960 rw-p 12288 0 4K com STACK-1696937-GC-Thread -
0x0000ec25813db000-0x0000ec25813eb000 65536 ---p 0 0 4K com - -
0x0000ec25813eb000-0x0000ec25815e9000 2088960 rw-p 12288 0 4K com STACK-1696936-GC-Thread -
0x0000ec25815e9000-0x0000ec25815ed000 16384 ---p 0 0 4K - - -
0x0000ec25815ed000-0x0000ec25817e7000 2072576 rw-p 32768 0 4K com - -
0x0000ec2581808000-0x0000ec258180c000 16384 ---p 0 0 4K com STACK-1696934-Common-Cleaner -
0x0000ec258180c000-0x0000ec2581a06000 2072576 rw-p 94208 0 4K com STACK-1696934-Common-Cleaner -
0x0000ec2581a06000-0x0000ec2581a0a000 16384 ---p 0 0 4K com STACK-1696933-Notification-Thread -
0x0000ec2581a0a000-0x0000ec2581c04000 2072576 rw-p 12288 0 4K com STACK-1696933-Notification-Thread -
0x0000ec2581c04000-0x0000ec2581c08000 16384 ---p 0 0 4K com STACK-1696932-C1-CompilerThread0 -
0x0000ec2581c08000-0x0000ec2581e02000 2072576 rw-p 20480 0 4K com STACK-1696932-C1-CompilerThread0 -
0x0000ec2581e02000-0x0000ec2581e06000 16384 ---p 0 0 4K com STACK-1696931-C2-CompilerThread0 -
0x0000ec2581e06000-0x0000ec2584000000 35627008 rw-p 32768 0 4K com GC -
0x0000ec2584000000-0x0000ec2584021000 135168 rw-p 4096 0 4K - - -
0x0000ec2584021000-0x0000ec2588000000 66973696 ---p 0 0 4K - - -
0x0000ec2588000000-0x0000ec2588021000 135168 rw-p 4096 0 4K - - -
0x0000ec2588021000-0x0000ec258c000000 66973696 ---p 0 0 4K - - -
0x0000ec258c000000-0x0000ec258c021000 135168 rw-p 12288 0 4K - - -
0x0000ec258c021000-0x0000ec2590000000 66973696 ---p 0 0 4K - - -
0x0000ec2590020000-0x0000ec259002c000 49152 r-xp 49152 0 4K com - /big/jdks/jdk24/lib/libnet.so
0x0000ec259002c000-0x0000ec259003b000 61440 ---p 0 0 4K com - /big/jdks/jdk24/lib/libnet.so
0x0000ec259003b000-0x0000ec259003c000 4096 r--p 4096 0 4K com - /big/jdks/jdk24/lib/libnet.so
0x0000ec259003c000-0x0000ec259003d000 4096 rw-p 4096 0 4K com - /big/jdks/jdk24/lib/libnet.so
0x0000ec2590040000-0x0000ec2590044000 16384 ---p 0 0 4K com STACK-1696930-Monitor-Deflation-Thread -
0x0000ec2590044000-0x0000ec259023e000 2072576 rw-p 12288 0 4K com STACK-1696930-Monitor-Deflation-Thread -
0x0000ec259023e000-0x0000ec2590242000 16384 ---p 0 0 4K com STACK-1696929-Service-Thread -
0x0000ec2590242000-0x0000ec259043c000 2072576 rw-p 12288 0 4K com STACK-1696929-Service-Thread -
0x0000ec259043c000-0x0000ec2590440000 16384 ---p 0 0 4K com STACK-1696928-Signal-Dispatcher -
0x0000ec2590440000-0x0000ec259063a000 2072576 rw-p 12288 0 4K com STACK-1696928-Signal-Dispatcher -
0x0000ec259063a000-0x0000ec259063e000 16384 ---p 0 0 4K com STACK-1696927-Finalizer -
0x0000ec259063e000-0x0000ec2590838000 2072576 rw-p 90112 0 4K com STACK-1696927-Finalizer -
0x0000ec2590838000-0x0000ec259083c000 16384 ---p 0 0 4K com STACK-1696926-Reference-Handler -
0x0000ec259083c000-0x0000ec2590a36000 2072576 rw-p 94208 0 4K com STACK-1696926-Reference-Handler -
0x0000ec2590a36000-0x0000ec2590a46000 65536 ---p 0 0 4K com - -
0x0000ec2590a46000-0x0000ec2590c44000 2088960 rw-p 16384 0 4K com STACK-1696925-VM-Thread -
...
0x0000ec2591470000-0x0000ec2591480000 65536 ---p 0 0 4K com - -
0x0000ec2591480000-0x0000ec259167e000 2088960 rw-p 12288 0 4K com STACK-1696921-GC-Thread -
0x0000ec259167e000-0x0000ec259168e000 65536 ---p 0 0 4K com - -
0x0000ec259168e000-0x0000ec259188c000 2088960 rw-p 12288 0 4K com - -
0x0000ec259188c000-0x0000ec259189c000 65536 ---p 0 0 4K com - -
0x0000ec259189c000-0x0000ec259207a000 8249344 rw-p 12288 0 4K com STACK-1696919-GC-Thread,GC -
0x0000ec259207a000-0x0000ec259783a000 92012544 ---p 0 0 4K - GC -
0x0000ec259783a000-0x0000ec2597906000 835584 rw-p 770048 0 4K com GC -
0x0000ec2597906000-0x0000ec25983fe000 11501568 ---p 0 0 4K - GC -
0x0000ec25983fe000-0x0000ec2598400000 8192 rw-p 8192 0 4K com GC -
0x0000ec2598400000-0x0000ec2598670000 2555904 rwxp 651264 0 4K com CODE -
0x0000ec2598670000-0x0000ec259f937000 120352768 ---p 0 0 4K - CODE -
0x0000ec259f937000-0x0000ec259fba7000 2555904 rwxp 626688 0 4K com CODE -
0x0000ec259fba7000-0x0000ec259fec7000 3276800 ---p 0 0 4K - CODE -
0x0000ec259fec7000-0x0000ec25a0137000 2555904 rwxp 237568 0 4K com CODE -
0x0000ec25a0137000-0x0000ec25a7400000 120360960 ---p 0 0 4K - CODE -
0x0000ec25a7400000-0x0000ec25afe3e000 144957440 r--s 1114112 0 4K com - /big/jdks/jdk24/lib/modules
0x0000ec25afe40000-0x0000ec25afe50000 65536 r--s 65536 0 4K com - /tmp/bigfile