btree_prune_min_interval- tunable to change the minimum time (seconds)
between consecutive btree prunes
The tunable sets the minimum time in seconds between reclaiming memory
used by a kernel data structure to represent file pages
Pages of a file are tracked by kernel data structures called btrees.
Depending on size of the file, the size of btree can also vary. Memory
consumed by these data structures will have an impact on the amount of
memory available for real application purposes. Some or all of the mem‐
ory used by these data structures can be freed back, if the pages the
files represent are reduced.
This activity is called pruning the btrees. If the pruning is not done
on a periodic basis, this can cause kernel memory pressure. On the
other hand if the pruning is done very frequently, this can cause per‐
formance issues for workloads which read/write large files frequently,
as these data structures need to be re-created to track the file pages.
This tunable helps to decide the next pruning time. Next prune time is
a random value which can vary between btree_prune_min_interval seconds
to 300 seconds. When to prune next time is determined after a success‐
ful btree prune. This random pruning helps to avoid fcache daemon to
monopolize the cpu resources.
must be a positive integer, between 60 and 300.
Who Is Expected to Change This Tunable?
Administrators interested in the kernel dynamic memory consumption and
the associated performance issues.
Restrictions on Changing
Changes to this tunable takes effect immediately.
When Should the Value of This Tunable Be Increased?
If the workload involves very active large files and kernel memory con‐
sumption is less
When Should the Value of This Tunable Be Lowered?
When the kernel memory consumption is very high. It is advised not to
change the default value unless it is absolutely necessary. The side-
effect of reducing the tunable value may result in frequent pruning by
fcache daemon which may monopolize the cpu resources.
When does this tunable change take effect?
Changes to this tunable take effect immediately without any reboot.
An invalid value is entered that is less than 60 and greater than 300.
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 ALSOkctune(1), kmem_aggressive_caching(5).
Tunable Kernel Parameterbtree_prune_min_interval(5)