Linux--- 手工释放系统cache

linux:/etc/rc.d # vmstat

procs -----------memory---------- ---swap-- -----io---- -system-- -----cpu------

 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st

 0  0      0 4205280  14880 2598540    0    0     0    12   11  12  0  1 98  1  0

这个cache是系统从物理内存分配一块，用来做文件系统的读缓冲，按照Linux的说明在系统内存紧张时，这个内存是会自动释放的。手工释放caches的方法：

sync;echo 3>/proc/sys/vm/drop_caches

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_caches

To free dentries and inodes:

* echo 2 > /proc/sys/vm/drop_caches

To free pagecache, dentries and inodes:

* echo 3 > /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 2.6.16.