ZGC

背景

昨天临下班同事贴了张top的图，在测试过程中进程 VIRT 项异常的高

测试机器是新到手的 Rocky Linux release 8.5 kernel 4.18，刚好我也有这台机器的权限，就爬上去看一眼。

step….s

1. top

• 和同事截图一致，VIRT 200G+，基于之前的印象第一感觉是不是程序线程开多了，一个线程 64M
• 拿到 processId，继续检查

2. cat /proc/9432/status

Name:   java
Umask:  0022
State:  S (sleeping)
Tgid:   9432
Ngid:   0
Pid:    9432
VmPeak: 212897896 kB
VmSize: 212884428 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:  11635800 kB
VmRSS:  11635800 kB
RssAnon:          613024 kB
RssFile:           24524 kB
RssShmem:       10998252 kB
VmData:   817140 kB
VmStk:       132 kB
VmExe:         4 kB
VmLib:     23368 kB
VmPTE:     24832 kB
VmSwap:        0 kB
HugetlbPages:          0 kB
Threads:        84
...
...

• 84个线程，算下来也不该这么大的占用

3. pmap -x 9432 or cat /proc/9432/maps

[root@localhost xxxxx]# cat /proc/9432/stat
9432 (java) S 1 9424 7983 34816 9886 1077952512 2169485 0 48 0 47084 41243 0 0 20 0 85 0 2341714 217993654272 3035148 18446744073709551615 93986510553088 93986510556840 140733418035776 0 0 0 0 3 16800972 0 0 0 17 2 0 0 5 0 0 93986510564600 0733418041311 0
[root@localhost xxxxx]# cat /proc/9432/maps
800000000-800003000 rwxp 00001000 08:03 67125341                         /opt/jdk-15.0.1/lib/server/classes_nocoops.jsa
800003000-8003e6000 rw-p 00004000 08:03 67125341                         /opt/jdk-15.0.1/lib/server/classes_nocoops.jsa
8003e6000-800b23000 r--p 003e7000 08:03 67125341                         /opt/jdk-15.0.1/lib/server/classes_nocoops.jsa
800b23000-800b24000 ---p 00000000 00:00 0 
800b24000-8014e4000 rw-p 00000000 00:00 0 
8014e4000-810324000 ---p 00000000 00:00 0 
40000000000-40100000000 rw-s 00000000 00:01 423464                       /memfd:java_heap (deleted)
40100000000-41000000000 ---p 00000000 00:00 0 
80000000000-80100000000 rw-s 00000000 00:01 423464                       /memfd:java_heap (deleted)
80100000000-81000000000 ---p 00000000 00:00 0 
100000000000-100100000000 rw-s 00000000 00:01 423464                     /memfd:java_heap (deleted)
100100000000-101000000000 ---p 00000000 00:00 0 
557af0934000-557af0935000 r-xp 00000000 08:03 67125607                   /opt/jdk-15.0.1/bin/java
557af0936000-557af0937000 r--p 00001000 08:03 67125607                   /opt/jdk-15.0.1/bin/java
557af0937000-557af0938000 rw-p 00002000 08:03 67125607                   /opt/jdk-15.0.1/bin/java
557af12e5000-557af19ed000 rw-p 00000000 00:00 0                          [heap]
...
...

[root@localhost qa_winter-game-battle]# pmap -x 9432
9432:   java -Dfile.encoding=UTF-8 -Denv=dev -Dapollo.cluster=dev -Deureka.client.registerWithEureka=false -Xms4g -Xmx4g -XX:+UseZGC -XX:MaxMetaspaceSize=256m -XX:MaxDirectMemorySize=1g -Xlog:gc*:./logs/gc.log -ea -jar game-battle.jar
Address           Kbytes     RSS   Dirty Mode  Mapping
0000000800000000      12       8       4 rwx-- classes_nocoops.jsa
0000000800003000    3980    1760      20 rw--- classes_nocoops.jsa
00000008003e6000    7412       0       0 r---- classes_nocoops.jsa
0000000800b23000       4       0       0 -----   [ anon ]
0000000800b24000    9984    9632    9040 rw---   [ anon ]
00000008014e4000  243968       0       0 -----   [ anon ]
0000040000000000 4194304 3407192 3407192 rw-s- memfd:java_heap (deleted)
0000040100000000 62914560       0       0 -----   [ anon ]
0000080000000000 4194304 3357220 3357220 rw-s- memfd:java_heap (deleted)
0000080100000000 62914560       0       0 -----   [ anon ]
0000100000000000 4194304 3356636 3356636 rw-s- memfd:java_heap (deleted)
0000100100000000 62914560       0       0 -----   [ anon ]
0000557af0934000       4       0       0 r-x-- java
0000557af0936000       4       0       0 r---- java
0000557af0937000       4       0       0 rw--- java
0000557af12e5000   38776   21236   21232 rw---   [ anon ]
...
...

• 看到了三块很大的分配， 加起来 180G；这块内存的位置看起来更像是进程启动所需的堆空间
  Address Kbytes RSS Dirty Mode Mapping
0000100100000000 62914560 0 0 ----- [ anon ]
0000100100000000 62914560 0 0 ----- [ anon ]
0000100100000000 62914560 0 0 ----- [ anon ]

• 这里也注意到，程序启动特别设置了 +UseZGC