Supporting Doc :
Actual memory , which is used by system runtime :
# grep PageTables /proc/meminfo
PageTables: 1244880 kB
Default Settings :
$ grep Huge /proc/meminfo
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
hugePage Script to find out the recommended settings :
#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the
# recommended HugePages/HugeTLB configuration
#
# Note: This script does calculation for all shared memory
# segments available when the script is run, no matter it
# is an Oracle RDBMS shared memory segment or not.
# Check for the kernel version
KERN=`uname -r | awk -F. '{ printf("%d.%d\n",$1,$2); }'`
# Find out the HugePage size
HPG_SZ=`grep Hugepagesize /proc/meminfo | awk {'print $2'}`
# Start from 1 pages to be on the safe side and guarantee 1 free HugePage
NUM_PG=1
# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | awk {'print $5'} | grep "[0-9][0-9]*"`
do
MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
if [ $MIN_PG -gt 0 ]; then
NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
fi
done
# Finish with results
case $KERN in
'2.4') HUGETLB_POOL=`echo "$NUM_PG*$HPG_SZ/1024" | bc -q`;
echo "Recommended setting: vm.hugetlb_pool = $HUGETLB_POOL" ;;
'2.6' | '3.8' | '3.10' | '4.1' ) echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
*) echo "Unrecognized kernel version $KERN. Exiting." ;;
esac
# End
Recommended setting for number of HugePages :
$ ./hugepages_setting.sh
Recommended setting: vm.nr_hugepages = 305
$
1)
Set this value to /etc/sysctl.conf :
vm.nr_hugepages=306
sysctl –p
2) Add the
following entries into the "/etc/security/limits.conf" script or
"/etc/security/limits.d/99-grid-oracle-limits.conf" script, where the
setting is at least the size of the HugePages allocation in KB (HugePages *
Hugepagesize). In this case the value is 306*2048=626688.
* soft memlock 626688
* hard memlock 626688
Check
the MEMORY_TARGET parameters are not set for the database and SGA_TARGET and
PGA_AGGREGATE_TARGET parameters are being used instead.
3)Restart the server and restart the database services as required.
Check the HugePages information again.
$ grep Huge /proc/meminfo
AnonHugePages: 0 kB
HugePages_Total: 306
HugePages_Free: 98
HugePages_Rsvd: 93
HugePages_Surp: 0
Hugepagesize: 2048 kB
$
Force Oracle to use HugePages (USE_LARGE_PAGES)
Sizing the number of HugePages correctly is important because
prior to 11.2.0.3, if the whole SGA doesn't fit into the available HugePages,
the instance will start up without using any. From 11.2.0.3 onward, the SGA can
run partly in HugePages and partly not, so the impact of this issue is not so
great. Incorrect sizing may not be obvious to spot. Later releases of the
database display a "Large Pages Information" section in the alert log
during startup.
****************** Large Pages Information *****************
Total Shared Global Region in Large Pages = 602 MB (100%)
Large Pages used by this instance: 301 (602 MB)
Large Pages unused system wide = 5 (10 MB) (alloc incr 4096 KB)
Large Pages configured system wide = 306 (612 MB)
Large Page size = 2048 KB
***********************************************************
If you are running Oracle 11.2.0.2 or later, you can set the USE_LARGE_PAGES initialization
parameter to "only" so the database fails to start if it is not
backed by hugepages. You can read more about this here.
ALTER SYSTEM SET use_large_pages=only SCOPE=SPFILE;
SHUTDOWN IMMEDIATE;
STARTUP;
On startup the "Large Page Information" in the alert log
reflects the use of this parameter.
****************** Large Pages Information *****************
Parameter use_large_pages = ONLY
Total Shared Global Region in Large Pages = 602 MB (100%)
Large Pages used by this instance: 301 (602 MB)
Large Pages unused system wide = 5 (10 MB) (alloc incr 4096 KB)
Large Pages configured system wide = 306 (612 MB)
Large Page size = 2048 KB
***********************************************************
Attempting to start the database when there aren't enough
HugePages to hold the SGA will now return the following error.
SQL> STARTUP
ORA-27137: unable to allocate large pages to create a shared memory segment
Linux-x86_64 Error: 12: Cannot allocate memory
SQL>
The "Large Pages Information" section of the alert log
output describes the startup failure and the appropriate action to take.
****************** Large Pages Information *****************
Parameter use_large_pages = ONLY
Large Pages unused system wide = 0 (0 KB) (alloc incr 4096 KB)
Large Pages configured system wide = 0 (0 KB)
Large Page size = 2048 KB
ERROR:
Failed to allocate shared global region with large pages, unix errno = 12.
Aborting Instance startup.
ORA-27137: unable to allocate Large Pages to create a shared memory segment
ACTION:
Total Shared Global Region size is 608 MB. Increase the number of
unused large pages to atleast 304 (608 MB) to allocate 100% Shared Global
Region with Large Pages.
***********************************************************
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