base_pagesize(5) File Formats Manual base_pagesize(5)
NAME
base_pagesize - size (in kilobytes) of a base page
VALUES
Default
Allowed values
DESCRIPTION
A base page is the smallest block of physical memory that can be allocated for storing data and code by the HP-UX kernel. Base pages are
also the smallest unit of memory protection.
The kernel maintains a number of tables, each of which has one entry for each base page. In large-memory systems, this can result in a
significant amount of physical memory being consumed by these tables. When a larger base page size is selected, fewer entries are required,
and therefore more physical memory becomes available for other uses.
Who is Expected to Change This Tunable?
The system administrator who wants to change the size of a base page.
Restrictions on Changing
Changes to this tunable require a reboot to take effect.
When Should the Value of This Tunable Be Raised?
To decrease the amount of memory consumed by kernel memory management tables.
What Are the Side Effects of Raising the Value?
Programs with small text and/or data segments will consume more memory that they would otherwise. This is because at least one base page
is allocated for each of these segments.
Memory fragmentation may also increase, which can lead to lower performance.
The value returned by the and system calls will reflect the base_pagesize setting of the currently running kernel. Applications which make
assumptions about the size of a base page, and do not call either or to obtain this value, may fail in unpredictable ways. See the white
paper referenced below for more details.
When Should the Value of This Tunable Be Lowered?
To reverse a situation in which the larger base page size has lowered performance or introduced application misbehavior.
What Are the Side Effects of Lowering the Value?
Kernel memory consumption will increase, due to larger tables being required to manage physical memory.
The larger tables may also result in lower performance in configurations which use large virtual pages aggressively.
What Other Tunables Should Be Changed at the Same Time?
Changes to and should be considered.
CONFIGURATION RESTRICTIONS
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 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
It is strongly recommended that systems configured with non-default settings of the tunable use only the VxFS filesytem to avoid problems
with HFS.
WARNINGS
Setting this tunable to other than the default can increase application and system performance. However, it can also cause some applica-
tions to fail. It is important to understand the tradeoffs described in the white paper before changing this tunable.
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of
HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by HP.
SEE ALSO
vps_pagesize(5), vps_ceiling(5).
There are more details in the white paper entitled located at
Tunable Kernel Parameters base_pagesize(5)