Linux 释放内存方法

[root@node1 ~]# free -m

total used free shared buffers cached

Mem: 8004 6557 1446 0 163 5630

-/+ buffers/cache: 763 7240

Swap: 1983 0 1983

其中：

total 内存总数

used 已经使用的内存数

free 空闲的内存数

shared 多个进程共享的内存总额

buffers Buffer Cache和cached Page Cache 磁盘缓存的大小

-buffers/cache 的内存数:used - buffers - cached

+buffers/cache 的内存数:free + buffers + cached

可用的memory=free memory+buffers+cached

把内存里的数据暂时写到硬盘里

[root@node1 ~]# sync

修改 /proc/sys/vm/drop_caches文件（/proc/sys/vm/drop_caches的默认值为0）

[root@node1 ~]# echo 3 > /proc/sys/vm/drop_caches

[root@node1 ~]# cat /proc/sys/vm/drop_caches

再看内存

[root@node1 ~]# free -m

total used free shared buffers cached

Mem: 8004 631 7372 0 0 60

-/+ buffers/cache: 570 7433

Swap: 1983 0 1983

终于释放出来了。

有关/proc/sys/vm/drop_caches的用法在下面进行了说明（原文：http://www.linuxinsight.com/proc_sys_vm_drop_caches.html）：

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 not freeable, the user should run "sync" first in order to make sure all cached objects are freed.

This tunable was added in 2.6.16.