pagezero_daemon_enabled(5)pagezero_daemon_enabled(5)NAMEpagezero_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 ALSOvps_ceiling(5).
Tunable Kernel Parameterspagezero_daemon_enabled(5)