base_pagesize(5)base_pagesize(5)NAMEbase_pagesize - size (in kilobytes) of a base page
A base page is the smallest block of physical memory that can be allo‐
cated 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 sig‐
nificant 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
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 perfor‐
The value returned by the and system calls will reflect the base_page‐
size 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 configura‐
tions which use large virtual pages aggressively.
What Other Tunables Should Be Changed at the Same Time?
Changes to and should be considered.
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
Setting this tunable to other than the default can increase application
and system performance. However, it can also cause some applications 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 parame‐
ter may be removed or have its meaning changed in future releases of
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 val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
was developed by HP.
SEE ALSOvps_pagesize(5), vps_ceiling(5).
There are more details in the white paper entitled located at
Tunable Kernel Parameters base_pagesize(5)