To free pagecache://释放页缓存
echo 1 > /proc/sys/vm/drop_caches
To free reclaimable slab objects (includes dentries and inodes)://释放inode和目录树缓存
echo 2 > /proc/sys/vm/drop_caches
To free slab objects and pagecache://包括1和2,即释放全部缓存
echo 3 > /proc/sys/vm/drop_caches