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 -m
total used free shared buffers cached
Mem:
-/+ buffers/cache:
Swap:   

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  > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo  > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo  > /proc/sys/vm/drop_caches
As 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..

修改/etc/sysctl.conf 添加如下选项后就不会内存持续增加

vm.dirty_ratio =
vm.dirty_background_ratio=
vm.dirty_writeback_centisecs=
vm.dirty_expire_centisecs=
vm.drop_caches=
vm.swappiness =
vm.vfs_cache_pressure=
vm.overcommit_memory=
vm.lowmem_reserve_ratio=
kern.maxvnodes=

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。