kmem_aggressive_caching.5 (2010 09)

k
kmem_aggressive_caching(5) kmem_aggressive_caching(5)
(Tunable Kernel Parameters)
NAME
kmem_aggressive_caching - policy hint for caching and pre-allocating pages underlying the kernel
dynamic memory
VALUES
Failsafe
0
Default
0
Allowed values
0-10
DESCRIPTION
The kmem_aggressive_caching
tunable provides a policy hint for favoring performance of kernel-
intensive workloads, by caching and pre-allocating physical pages underlying the kernel dynamic
memory.
kmem_aggressive_caching
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
kmem_aggressive_caching
. A change in the kmem_aggressive_caching
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 some-
time 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
kmem_aggressive_caching
, 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 ker-
nel 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
kmem_aggressive_caching 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 during 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
[EINVAL] 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 parameter may be removed or have its
meaning changed in future releases of HP-UX.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1