Shared Memory Tuning: startup database - ORA-27102: out of memory Linux-X86_64 Error: 28: No space left on device

SQL> startup

ORA-27102: out of memory

Linux-x86_64 Error: 28: No space left on device

I have used RHEL X86_64 + memory (32GB) and setted sga_max_size=20G + sga_target=20G and ...

$ cat /proc/sys/kernel/shmmax

26843545600

What wrong with my kernel tuning... So, I checked metalink (301830.1) and some recommend from RHEL

They told; set SHMALL to the total amount of physical RAM divided by page size.

SHMALL =>Total amount of shared memory available (bytes or pages)

then:

Check Page Size:

$ getconf PAGE_SIZE

4096

Determine the system wide maximum number of shared memory pages:

$ cat /proc/sys/kernel/shmall

2097152

My system 64bits with memory 32GB, then 1024 * 1024 * 1024 * 32 / 4096 = 8388608

So, change kernel.shmall = 8388608

$ su - root

# echo 8388608 > /proc/sys/kernel/shmall

Or modify /etc/sysctl.conf file:

kernel.shmall=8388608

and

# sysctl -p

After changed... check and startup database again:

$ cat /proc/sys/kernel/shmall

8388608

SQL> startup

.

.

.

--- NO ERROR ---

By the way, I read Tuning Red Hat Enterprise Linux: Oracle and Oracle RAC

From this idea with memory 32GB

mem=$(free|grep Mem|awk '{print$2}')

totmem=$(echo "$mem*1024"|bc)

huge=$(grep Hugepagesize /proc/meminfo|awk '{print $2}')

max=$(echo "$totmem*75/100"|bc)

all=$(echo "$max/$huge"|bc)

echo "kernel.shmmax = $max"

echo "kernel.shmall = $all"

Result:

kernel.shmmax = 25213120512, kernel.shmall = 12311094

However, This case "ORA-27102: out of memory Linux-X86_64 Error: 28: No space left on device" , solved by set SHMALL = MemTotal(byte)/PAGE_SIZE

and ...

I hope to hear your idea about kernel tuning with Oracle Database.