Linux下清理内存和Cache方法 /proc/sys/vm/drop_caches

Linux下清理内存和Cache方法 /proc/sys/vm/drop_caches

频繁的文件访问会导致系统的Cache使用量大增

$ free -mtotal used free shared buffers cachedMem: 3955 3926 28 0 55 3459-/+ buffers/cache: 411 3544Swap: 5726 0 5726

 

free内存减少到几十兆，系统运行缓慢

运行sync将dirty的内容写回硬盘
$sync

通过修改proc系统的drop_caches清理free的cache
$echo 3 > /proc/sys/vm/drop_caches

drop_caches的详细文档如下：

Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.To free pagecache:* echo 1 > /proc/sys/vm/drop_cachesTo free dentries and inodes:* echo 2 > /proc/sys/vm/drop_cachesTo free pagecache, dentries and inodes:* echo 3 > /proc/sys/vm/drop_cachesAs this is a non-destructive operation, and dirty objects are notfreeable, the user should run "sync" first in order to make sure allcached objects are freed.This tunable was added in 2.6.16.

 

修改/etc/sysctl.conf 添加如下选项后就不会内存持续增加

vm.dirty_ratio = 1vm.dirty_background_ratio=1vm.dirty_writeback_centisecs=2vm.dirty_expire_centisecs=3vm.drop_caches=3vm.swappiness =100vm.vfs_cache_pressure=163vm.overcommit_memory=2vm.lowmem_reserve_ratio=32 32 8kern.maxvnodes=3

 

上面的设置比较粗暴，使cache的作用基本无法发挥。需要根据机器的状况进行适当的调节寻找最佳的折衷。