fcache_vhand_ctl(5)fcache_vhand_ctl(5)NAMEfcache_vhand_ctl - file cache policy control for the system pager dae‐
The tunable is used to determine the aggressiveness of the system pager
daemon with respect to flushing the file pages from the file cache.
must be a positive integer between 0 and 10, 0 being the default.
In general, the system pager daemon behaves more aggressively for
higher values of A change in the value may have a direct impact on sys‐
tem throughput and response times.
If the system pager daemon is not aggressive, less free memory may be
available in the file cache, and a file I/O intensive application may
observe a loss in performance. If the paging daemon is too aggressive,
the system may observe thrashing, and the CPU utilization by the system
pager daemon may increase.
Customers must evaluate the performance impact in their workload envi‐
ronment before changing the value of this tunable from the default
value on production systems. To determine a reasonable value for you
should consider the file system I/O-intensive applications on your sys‐
tem, the I/O responsiveness needed, the I/O throughput required, and
the permissible CPU utilization by the system pager daemon.
You should also consider changes to and before modifying See file‐
cache_min(5) and filecache_max(5).
Who Is Expected to Change This Tunable?
Administrators investigating the performance characteristics of file
I/O intensive workloads.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Raised?
Confirm the and values are sufficient for an I/O intensive application
before raising this tunable.
The tunable should be raised when the system suffers from low I/O
responsiveness of and low I/O throughput. The tunable should be exer‐
cised with extreme caution as it will have a direct impact on system
throughput and response times. In most case, the default value should
What are the Side Effects of Raising the Value?
Increasing the value should increase the CPU utilization of the system
pager daemon and may vary the I/O throughput.
When Should the Value of This Tunable Be Lowered?
The tunable should be lowered when the system seems to spend most of
it's time running the the system pager daemon.
What are the Side Effects of Lowering the Value?
The I/O responsiveness may decrease and the I/O throughput may vary.
What Other Tunable Values Should Be Changed at the Same Time?
An invalid value is entered that is not an integer
between 0 and 10, such as a negative number.
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 HP-UX Release Notes at
was developed by HP.
SEE ALSOfilecache_min(5), filecache_max(5).
Tunable Kernel Parameters fcache_vhand_ctl(5)