以下来自于官方文档：

kernel.shmall = physical RAM size / pagesize For most systems, this will be the value 2097152. See Note 301830.1 for more information.

kernel.shmmax = 1/2 of physical RAM. This would be the value 2147483648 for a system with 4GB of physical RAM. See Note:567506.1 for more information

查询系统pagesize的方法：

oracle@cpty01:~> getconf PAGESIZE

4096

64G物理内存kernel.shmall参数的计算为：64*1024*1024*1024/4096=16777216