base_pagesize.5 (2010 09)

b
base_pagesize(5) base_pagesize(5)
(Tunable Kernel Parameters)
NAME
base_pagesize - size (in kilobytes) of a base page
VALUES
Default
4
Allowed values
4 (minimum)
8
16
64 (maximum)
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
getpagesize()
and sysconf(_SC_PAGE_SIZE) 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
getpagesize()
or sysconf(_SC_PAGE_SIZE) 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 applica-
tion 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
vps_pagesize and vps_ceiling 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
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.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1