修改/proc/sys/vm/drop_caches，释放Slab占用的cache内存空间（参考drop_caches的官方文档）：

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.

linux服务器占用内存过高，首先使用free -m查看内存使用情况，再使用top命令，shift+M按内存排序后，查看具体是哪个进程占用太多的内存。

处理方法：

1、执行sync命令强制将内存中的文件缓冲内容写到磁盘

2、执行以下命令来释放pagecache, dentries and inodes

echo 3 > /proc/sys/vm/drop_caches