fcache_vhand_ctl.5 (2010 09)

f
fcache_vhand_ctl(5) fcache_vhand_ctl(5)
(Tunable Kernel Parameters)
NAME
fcache_vhand_ctl - file cache policy control for the system pager daemon
VALUES
Failsafe
0
Default
0
Allowed values
0-10
Recommended values
Default value
DESCRIPTION
The
fcache_vhand_ctl
tunable is used to determine the aggressiveness of the system pager daemon
with respect to flushing the file pages from the file cache.
fcache_vhand_ctl
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
fcache_vhand_ctl. A change in the
fcache_vhand_ctl 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 environment before changing the
value of this tunable from the default value on production systems. To determine a reasonable value for
fcache_vhand_ctl, you should consider the file system I/O-intensive applications on your system, the
I/O responsiveness needed, the I/O throughput required, and the permissible CPU utilization by the sys-
tem pager daemon.
You should also consider changes to
filecache_min
and filecache_max before modifying
fcache_vhand_ctl
. See filecache_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
filecache_min and filecache_max values are sufficient for an I/O intensive applica-
tion before raising this tunable.
The tunable should be raised when the system suffers from low I/O responsiveness of
read()/write()
and low I/O throughput. The tunable should be exercised with extreme caution as it will have a direct
impact on system throughput and response times. In most case, the default value should be sufficient.
What are the Side Effects of Raising the Value?
Increasing the
fcache_vhand_ctl value should increase the CPU utilization of the system pager dae-
mon 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?
None
ERRORS
[EINVAL] An invalid value is entered that is not an integer between 0 and 10, such as a negative
number.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1