shmmax: Maximum size of shared memory segment (bytes)
shmmin: Minimum size of shared memory segment (bytes)
shmall: Total amount of shared memory available (bytes or pages)
shmseg: Maximum number of shared memory segments per process
shmmni: Maximum number of shared memory segments system-wide

semmni: Maximum number of semaphore identifiers
semmns: Maximum number of semaphores system-wide
semmsl: Maximum number of semaphores per set
semmap: Number of entries in semaphore map
semvmx: Maximum value of semaphore

kernel.shmall和kernel.shmmax这两个值可以设置为内存的 90%。
kernel.shmmax = Total Physical Memory * 90%
kernel.shmall = kernel.shmmax / kernel.shmmni

# semaphores: semmsl, semmns, semopm, semmni
kernel.sem = 250 32000 100 128

shmmax: 250KB + 8.2KB * Shared_Buffers + 14.2KB * MAX_CONNECTIONS or INFINITY
shmmin: 1
shmall: if bytes, same as SHMMAX; if pages, ceil(SHMMAX/PAGE_SIZE)
shmseg: only 1 segment is needed, but the default is much higher
shmmni: like SHMSEG plus room for other applications

semmni: >=ceil(MAX_CONNECTIONS/16)
semmns: ceil(MAX_CONNECTIONS/16) * 17 + room for other applications
semmsl: >=17
semmap:
semvmx: >=255 (The default is oftern 32767, don't change unless asked to.)

获得PAGE_SIZE大小： getconf PAGE_SIZE

可以为Oracle分配多个共享段以满足SGA设置的需要
$ ipcs -sa
$ ps -ef | grep 3102      -- PID = 3102
$ pmap 3102

kernel.shmmni = 4096    页大小
kernel.shmmax = 2147483648   单个内存共享段的最大大小
kernel.shmall = 2097152  系统中内存共享段所能使用的最大大小，可以用物理内存除以页大小 来计算出来

ZT：http://wajoynece.cn/tag/shmmni/