HP-UX Reference (11i v2 03/08) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

n
dnlc_hash_locks(5) dnlc_hash_locks(5)
(Tunable Kernel Parameters)
NAME
dnlc_hash_locks - number of locks for the Directory Name Lookup Cache (DNLC)
VALUES
Failsafe
512
Default
512
Allowed values
The minimum value allowed is 16. The maximum value allowed is
8192. The value is further con-
strained in that it must be be a power of 2, and it must be equal to or less than one eighth the number of
DNLC entries
(ncsize >= 8 * dnlc_hash_locks)
.
Specify a positive integer value.
DESCRIPTION
To speed up the search through directories in the kernel, there is a memory resident cache of directories
called the
Directory Name Lookup Cache (DNLC). During a filename lookup in the kernel, any
directories or files encountered are retained in the DNLC for future reference. The DLNC is managed in
a Least Recently Used (LRU) fashion. The dnlc_hash_locks
dictates the number of lock groups that
will be used to manage the directory entries in the DNLC hash chains.
Who Is Expected to Change This Tunable?
HP-UX system administrators.
Restrictions on Changing
This tunable is static. Any changes to the value of this tunable will require system reboot before taking
effect.
When Should the Value of This Tunable Be Raised?
The value may need to be raised to reduce lock contention and improve filename lookup performance
when running applications which require large numbers of filename access.
What are the Side Effects of Raising the Value?
More system memory will be consumed to allocate locks for the DNLC.
When Should the Value of This Tunable Be Lowered?
The value can be lowered to limit the number of locks allocated for the DNLC and reduce memory con-
sumption.
What are the Side Effects of Lowering the Value?
Less system memory will be consumed for the DNLC locks upon system reboot. Operations requiring
filename lookup (e.g. open(2)) may experience performance degradation.
What Other Tunable Values Should Be Changed at the Same Time?
The value of
ncsize must be equal to or greater than eight times the value of dnlc_hash_locks
(ncsize >= 8 * dnlc_hash_locks).
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.
AUTHOR
dnlc_hash_locks was developed by HP.
SEE ALSO
kctune(1M), sam(1M), gettune(2), settune(2), dnlc_hash_locks(5).
HP-UX 11i Version 2: August 2003 − 1 − Hewlett-Packard Company Section 5−−81