Huge Pages And Shared Memory File System In Red Hat Enterprise Linux 3 - Red Hat ENTERPRISE LINUX 5.1 - LINUX ORACLE Tuning Manual

Oracle 9i and 10g tuning guide
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Chapter 14. Large Memory Optimization, Big Pages, and Huge Pages
Note
In order that an Oracle database can use Huge Pages in Red Hat Enterprise Linux 4 or 5,
you also need to increase the ulimit parameter "memlock" for the oracle user in /etc/
security/limits.conf if "max locked memory" is not unlimited or too small, see
ulimit -a or ulimit -l. An example can be seen below.
oracle
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oracle
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The memlock parameter specifies how much memory the oracle user can lock into its address space.
Note that Huge Pages are locked in physical memory. The memlock setting is specified in KB and
must match the memory size of the number of Huge Pages that Oracle should be able to allocate.
So if the Oracle database should be able to use 512 Huge Pages, then memlock must be set to at
least 512 * Hugepagesize, which on this system would be 1048576 KB (512*1024*2). If memlock
is too small, then no single Huge Page will be allocated when the Oracle database starts. For more
information on setting shell limits, see
Log in as the oracle user again and verify the new memlock setting by executing ulimit -l before
starting the database.
After an Oracle DB startup you can verify the usage of Huge Pages by checking whether the number
of free Huge Pages has decreased:
$ grep HugePages_Free /proc/meminfo
To free the Huge Pages pool, you can execute:
# echo 0 > /proc/sys/vm/nr_hugepages
This command usually takes a while to finish.
14.8. Huge Pages and Shared Memory File System in Red
Hat Enterprise Linux 3
The following example shows that the Huge Pages pool is not being used by the ramfs shared
memory file systems. The ramfs shared memory file systems can be used for Configuring Very Large
Memory (VLM).
The ipcs command shows only System V shared memory segments. It does not display shared
memory of a shared memory file systems. The following command shows System V shared memory
segments on a node running a database with an SGA of 2.6 GB:
# ipcs -m
------ Shared Memory Segments --------
key
shmid
0x98ab8248 1081344
0xe2e331e4 1245185
The first shared memory segment of 74 MB was created by the ASM instance. The second shared
memory segment of 2.6 GB was created by the database instance.
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memlock
1048576
memlock
1048576
Chapter 22, Setting Shell Limits for Your Oracle
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