For large SGA sizes, HugePages can give substantial benefits in virtual memory management. Without HugePages, the memory of the SGA is divided into 4K pages, which have to be managed by the Linux kernel. Using HugePages, the page size is increased to 2MB (configurable to 1G if supported by the hardware), thereby reducing the total number of pages to be managed by the kernel and therefore reducing the amount of memory required to hold the page table in memory. In addition to these changes, the memory associated with HugePages can not be swapped out, which forces the SGA to stay memory resident. The savings in memory and the effort of page management make HugePages pretty much mandatory for Oracle systems running on x86-64 architectures. However their is a limitation by Oracle, because Automatic Memory Management (AMM) does not support HugePages. If you already use AMM and MEMORY_TARGET is set you have to disable it and switch back to Automatic Shared Memory Management (ASMM). That means set SGA_TARGET and PGA_AGGREGATE_TARGET.
1. To determine how much memory currently using to support the page table
[root@bo3udsmsxodb01 ~]# grep PageTables /proc/meminfo PageTables: 9764 kB
2. Check current HugePage usages
[root@bo3udsmsxodb01 ~]$ grep Huge /proc/meminfo AnonHugePages: 0 kB ShmemHugePages: 0 kB FileHugePages: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Hugetlb: 0 kB
3. This script is intended to compute values for the recommended HugePages configuration
#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the
# recommended HugePages/HugeTLB configuration
# on Oracle Linux
#
# 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.
#
# This script is provided by Doc ID 401749.1 from My Oracle Support
# http://support.oracle.com
# Welcome text
echo "
This script is provided by Doc ID 401749.1 from My Oracle Support
(http://support.oracle.com) where it is intended to compute values for
the recommended HugePages/HugeTLB configuration for the current shared
memory segments on Oracle Linux. Before proceeding with the execution please note following:
* For ASM instance, it needs to configure ASMM instead of AMM.
* The 'pga_aggregate_target' is outside the SGA and
you should accommodate this while calculating the overall size.
* In case you changes the DB SGA size,
as the new SGA will not fit in the previous HugePages configuration,
it had better disable the whole HugePages,
start the DB with new SGA size and run the script again.
And make sure that:
* Oracle Database instance(s) are up and running
* Oracle Database 11g Automatic Memory Management (AMM) is not setup
(See Doc ID 749851.1)
* The shared memory segments can be listed by command:
# ipcs -m
Press Enter to proceed..."
read
# 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 $2}'`
if [ -z "$HPG_SZ" ];then
echo "The hugepages may not be supported in the system where the script is being executed."
exit 1
fi
# Initialize the counter
NUM_PG=0
# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | cut -c44-300 | awk '{print $1}' | grep "[0-9][0-9]*"`
do
MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
if [ $MIN_PG -gt 0 ]; then
NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
fi
done
RES_BYTES=`echo "$NUM_PG * $HPG_SZ * 1024" | bc -q`
# An SGA less than 100MB does not make sense
# Bail out if that is the case
if [ $RES_BYTES -lt 100000000 ]; then
echo "***********"
echo "** ERROR **"
echo "***********"
echo "Sorry! There are not enough total of shared memory segments allocated for
HugePages configuration. HugePages can only be used for shared memory segments
that you can list by command:
# ipcs -m
of a size that can match an Oracle Database SGA. Please make sure that:
* Oracle Database instance is up and running
* Oracle Database 11g Automatic Memory Management (AMM) is not configured"
exit 1
fi
# 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') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'3.8') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'3.10') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'4.1') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'4.14') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'4.18') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
'5.4') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
*) echo "Kernel version $KERN is not supported by this script (yet). Exiting." ;;
esac
# End
4. Create a text file named hugepages_settings.sh and Copy above contents
5. Make hugepages_settings.sh as executable file
[root@bo3udsmsxodb01 ~]# chmod +x hugepages_settings.sh
6. Verify all the below requiremnet has been met to execute the hugepages_settings.sh
- Oracle Database instance(s) are up and running
- Automatic Memory Management (AMM) is not setup
- The shared memory segments can be listed by command "ipcs -m"
- Oracle Linux Package 'bc' installed
7. Run hugepages_settings.sh
[root@bo3udsmsxodb01 ~]# ./hugepages_settings.sh
8. Script return the computed value of HugePages.
[root@bo3udsmsxodb01 ~]# Recommended setting: vm.nr_hugepages = 16386
9. Modify /etc/sysctl.conf, Add 'vm.nr_hugepages = 16386' to end of the file and save
10. Run 'sysctl -p' effect the changes. Make sure the parameter and values are same as recommended
[root@bo3udsmsxodb01 ~]# sysctl -p fs.file-max = 6815744 kernel.sem = 250 32000 100 128 kernel.shmmni = 4096 kernel.shmall = 1073741824 kernel.shmmax = 4398046511104 kernel.panic_on_oops = 1 net.core.rmem_default = 262144 net.core.rmem_max = 4194304 net.core.wmem_default = 262144 net.core.wmem_max = 1048576 net.ipv4.conf.all.rp_filter = 2 net.ipv4.conf.default.rp_filter = 2 fs.aio-max-nr = 1048576 net.ipv4.ip_local_port_range = 9000 65500 vm.nr_hugepages = 16386
11. You can verify whether HugePages are created now
[root@bo3udsmsxodb01 ~]# grep Huge /proc/meminfo AnonHugePages: 0 kB ShmemHugePages: 0 kB FileHugePages: 0 kB HugePages_Total: 16386 HugePages_Free: 16386 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Hugetlb: 33558528 kB
Reference
