base_pagesize man page on HP-UX

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base_pagesize(5)					      base_pagesize(5)

       base_pagesize - size (in kilobytes) of a base page

   Allowed values
       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
       with HFS.

       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.

       vps_pagesize(5), vps_ceiling(5).

       There are more details in the white paper entitled located at

			   Tunable Kernel Parameters	      base_pagesize(5)

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