kmem_aggressive_caching(5)kmem_aggressive_caching(5)NAMEkmem_aggressive_caching - policy hint for caching and pre-allocating
pages underlying the kernel dynamic memory
VALUES
Failsafe
Default
Allowed values
DESCRIPTION
The tunable provides a policy hint for favoring performance of kernel-
intensive workloads, by caching and pre-allocating physical pages
underlying the kernel dynamic memory.
must be a positive integer between 0 and 10, 0 being the default.
In general, the kernel aggressively allocates large pages for higher
values of A change in the value may have a direct impact on number of
physical pages allocated for use by kernel objects.
If the kernel is not aggressive in using large pages for its objects,
then kernel intensive workloads may witness numerous TLB misses during
execution. If the kernel is too aggressive, the system could sometime
encounter a brief shortage of free physical memory, which could delay
application startup or cause page fault.
On production systems, customers must evaluate the performance impact
on their workload environment before changing the value of this tunable
from the default value. To determine a reasonable value for you should
consider the nature of the workload. A higher value may be useful for
those workloads that are highly kernel-intensive.
Who Is Expected to Change This Tunable?
Administrators investigating the performance characteristics of kernel
intensive workloads.
Restrictions on Changing
Changes to this tunable take effect immediately; however, the changes
would be effective only on new kernel memory allocations.
When Should the Value of This Tunable Be Raised?
The tunable should be raised when the system suffers from numerous TLB
misses while running kernel intensive workloads. In most cases, the
default value should be sufficient.
What are the Side Effects of Raising the Value?
Increasing the value would increase the number of pages allocated for
caching kernel objects.
When Should the Value of This Tunable Be Lowered?
The tunable should be lowered when applications suffer from delays dur‐
ing startup or page fault due to lack of free memory.
What are the Side Effects of Lowering the Value?
Certain workloads may incur more TLB misses.
What Other Tunable Values Should Be Changed at the Same Time?
None
ERRORS
An invalid value is entered that is not an integer
between 0 and 10, such as a negative number.
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 HP-UX Release Notes at
AUTHOR
was developed by HP.
SEE ALSOfcache_vhand_ctl(5), filecache_min(5), filecache_max(5).
Tunable Kernel Parameterskmem_aggressive_caching(5)
