pagezero_daemon_enabled man page on HP-UX

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pagezero_daemon_enabled(5)			    pagezero_daemon_enabled(5)

NAME
       pagezero_daemon_enabled	-  zeroing of free memory in the background is
       enabled

VALUES
   Default
   Allowed values
       Minimum:

       Maximum:

DESCRIPTION
       HP-UX provides improved security by zeroing  out	 any  memory  that  is
       being  assigned to user space.  This ensures that no user can read what
       may have been written by some other user.   Normally,  the  zeroing  is
       done  when the physical page is allocated to the user -- often when the
       application touches the page for the first  time.   Some	 system	 calls
       like  also  result  in  the zeroing of pages.  The time taken for these
       kind of system calls and accesses depends upon the size of  the	memory
       being  zeroed  out.  A 4G page may easily take many seconds to be allo‐
       cated.  A large database shared memory segment may take many minutes to
       be allocated.  Allocation of a small page is generally unobservable.

       The  daemon  is a performance enhancement that reduces the elapsed time
       for completing kernel operations like page faults, and so on.  The idea
       is  to  zero  out large free pages (4MB and above in size) during times
       when the CPU is idle.  The daemon has been specially designed to ensure
       that it only executes for brief times when the CPU is idle.

       However,	 under	certain	 conditions,  where some resource (CPU, TLB or
       Memory bandwidth) is very highly utilized,  it  is  possible  that  the
       operation of the daemon adversely impacts performance.  For example, if
       the application is limited by the memory bandwidth, then it may be bet‐
       ter  to	disable	 the  daemon.	This situation is expected to be rare.
       Most workloads will not need to disable the daemon.

       This tunable allows system administrators to  disable  and  enable  the
       daemon.	 Once  the  daemon has been disabled, it will not zero out any
       more pages.  Any pages already in the process of being zeroed  will  be
       zeroed  out.  When the daemon is enabled, it will zero out any unzeroed
       free pages of size 4MB and more.

   Who is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Changes to this tunable take effect immediately.

   When Should the Value of This Tunable Be Changed to 0?
       This tunable should be changed only if the system is using large	 pages
       (i.e.  is set to 4MB or above).	Changing it if the system is not using
       pages of size 4M and above will have no effect.	It may be changed to 0
       if  the system is bottle-necked on some hardware resource.  In particu‐
       lar, disabling the  daemon  may	help  in  decreasing  TLB  misses  and
       increasing the available CPU time and reducing memory latencies.

   What Are the Side Effects of changing the value to 0?
       Disabling  the  daemon  will increase the time it takes to process page
       faults and to complete system calls that result in  the	allocation  of
       memory (e.g.

WARNINGS
       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter 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 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

AUTHOR
       was developed by HP.

SEE ALSO
       vps_ceiling(5).

			   Tunable Kernel Parameterspagezero_daemon_enabled(5)
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