IBM WEBSPHERE 6.1.X User Manual

Page 12

W E B S P H E R E P O R T A L V 6 . 1 T U N I N G G U I D E

J V M H E A P L A R G E P A G E

Large pages can reduce the CPU overhead needed to keep track of heap. With this setting
we have seen 10% throughput improvement in our measurements.

This setting does improve performance on Windows, we did not set it for our measurements because
Portal doesn’t start reliably when –Xlp is set, sometimes it requires a system reboot to get the jvm to
start.

How-to Set: In the WebSphere Administrative Console: Servers -> Application Servers ->
WebSphere Portal -> Server Infrastructure: Java and Process Management -> Process Definition ->
Java Virtual Machine -> Generic JVM Argument. Add –Xlp.

Large pages are supported by systems running Linux kernels V2.6 or higher. See JVM
Large Page Tuning for AIX Operation System.

J V M L A R G E P A G E T U N I N G O N A I X O P E R A T I N G S Y S T E M

To use JVM Large Page, AIX operating system must be configured to support large pages.

How-To Set:

1. We use the following steps to allocate 4GB of RAM as large pages (16MB) . We chose

this amount based on having 8GB of physical memory in these systems. These values
may need to be adjusted on systems with different amounts of physical memory.

vmo -r -o lgpg_regions=256 -o lgpg_size=16777216

bosboot -ad /dev/ipldevice

reboot -q

vmo -p -o v_pinshm=1

chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE $USER

2. Add: -Xlp command-line option as described above.
3. In the WebSphere Administrative Console: Servers

Application Servers

WebSphere Portal

Server Infrastructure: Java and Process Management

Process

Definition-> Environment Entries New

EXTSHM=OFF (note: When EXTSHM is

on it prevents use of large page).

4. Restart Portal Server. To verify if large pages are being used, run the AIX command

vmstat -l 1 5 and check the "alp" column which is the active large page used. It should
be a non-zero value if large pages are being used.

Parameter

AIX

POWER5

Linux

Solaris

Windows

2003

z/Linux

z/OS

JVM Heap
Large page

-Xlp

Not
Applicable