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)