最近CDH集群频繁告警，原因是某些host频繁swapping，极大影响了集群的性能。
后来发现有个设置（/proc/sys/vm/swappiness）需要修改，默认值60
Setting the vm.swappiness Linux Kernel Parameter
vm.swappiness is a Linux Kernel Parameter that controls how aggressively memory pages are swapped to disk. It can be set to a value between 0-100; the higher the value, the more aggressive the kernel is in seeking out inactive memory pages and swapping them to disk.
You can see what value vm.swappiness is currently set to by looking at /proc/sys/vm; for example:
cat /proc/sys/vm/swappiness
On most systems, it is set to 60 by default. This is not suitable for Hadoop clusters nodes, because it can cause processes to get swapped out even when there is free memory available. This can affect stability and performance, and may cause problems such as lengthy garbage collection pauses for important system daemons. Cloudera recommends that you set this parameter to 0; for example:
# sysctl -w vm.swappiness=0