linux清理Cache

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 not freeable, the

user should run `sync' first.