Tunable Base Page Size

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Updating applications
While most applications are not sensitive to the base page size, some applications will not operate
properly when the base page size is tuned to a value larger than the default. Some applications
implicitly assume that the size of a base page is 4 kB. This assumption may lead to inappropriate
sizes for data objects created by the application. For example, an application under an object size
constraint of 1 MB, may incorrectly assume that an object whose size is 200 pages is smaller than the
1 MB limit. Instructions for application programmers to make their code independent of base page
size are given in the appendix Application programming for tunable base pages.
It is also possible for applications that don't depend directly on the base page size to have problems
when used with large base pages. For example, the increase in object size due to rounding to a
page boundary can cause stack overflow. This is likely only for applications whose stack size is
adjusted to a value smaller than the default.
HP has not validated that all third-party applications and drivers work properly with large base
pages. For that reason, the kctune command displays a warning message when base_pagesize
is tuned to a value larger than 4. System administrators are advised to conduct controlled
experiments with their entire application stack before tuning the base page size to a value larger than
the default.
Known limitations
Java Virtual Machine
Earlier versions of the Java Virtual Machine do not operate properly with large base pages. The
versions delivered with Update 3, and the latest versions available via Web release, work correctly at
all base page sizes. For the 1.4 release stream, version 1.4.2.19 is the minimum version required for
large base pages. For the version 5 release stream, version 5.0.13 (also called 1.5.0.13) is
required. The version 6 release stream, starting with version 6.0.1, works correctly at all base page
sizes.
Some applications bundle the Java Virtual Machine with their application distribution. That is, even
though the system may have the most current Java version, the application points to a Java directory
that was installed along with the application. If the bundled Java version is older than the minimum
required version, the application will not operate properly with large base pages. List of such
applications identified by HP is given in the appendix Application Compatibility. It is possible that
additional applications also bundle older Java versions.
HFS Filesystem
The HFS filesystem does not support configurations where the HFS block size is smaller than the
system base page size. Misconfigured HFS filesystems will cause the mount command to fail.
There are two ways to avoid this problem:
1. Use only VxFS filesystems (the preferred solution).
2. Make your HFS filesystems with blksize=64k, fragsize=8k.
It is strongly recommended that systems configured with non-default settings of the base_pagesize
parameter use only the VxFS filesystem to avoid problems with HFS.
Information on how to convert existing HFS filesystems to VxFS can be found in the HP-UX 11i v2
manual, “HP Servers and Workstations: Managing Systems and Workgroups, A Guide for HP-UX
System Administrators”, at http://docs.hp.com.