pagezero_daemon_enabled(5)					File Formats Manual					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 unobserv-
       able.

       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
       better 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 unze-
       roed 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
       particular, 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 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_ceiling(5).

							     Tunable Kernel Parameters					pagezero_daemon_enabled(5)