理解overcommit_memory

Redis在启动的时候会报如下WARNING：

WARNING overcommit_memory is set to 0! Background save may failunder low memory condition.

To fix this issue add 'vm.overcommit_memory = 1'to /etc/sysctl.conf and then reboot or run the command 'sysctlvm.overcommit_memory=1' for this to take effect.

java -Xmx20g -version

Error occurred during initialization of VM

Could not reserve enough space for object heap

Could not create the Java virtual machine.

但是给10g的时候就OK

java -Xmx10g -version

java version "1.6.0_37"

Java(TM) SE Runtime Environment (build 1.6.0_37-b06)

Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01, mixed mode)

内存明明是够的，后来发现在这台服务器上overcommit_memory被设置了2：

cat /proc/meminfo |grep -i commit

CommitLimit(=memory*overcommit_ratio+swap):49744512 kB

Committed_AS: 33947660 kB

从上面可知只能再分配不到14GB的空间，因此也就解释了上面的这个错误，后改成0解决；

本文转自MIKE老毕 51CTO博客，原文链接：http://blog.51cto.com/boylook/1299870，如需转载请自行联系原作者