filecache_max.5 (2010 09)

ﬁlecache_max(5) ﬁlecache_max(5)

(Tunable Kernel Parameters)

What Are the Side Effects of Raising the Values?

The amount of memory reserved for the minimum ﬁle cache size, dictated by

filecache_min

, cannot

be used on the system for other purposes. Be careful not to raise this value so high that it can eventually

cause memory pressure and overall system performance degradation.

When Should the Values of These Tunables Be Lowered?

The value of the minimum limit,

filecache_min

, can be lowered to allow a larger percentage of

memory to be used for purposes other than ﬁlesystem I/O caching, depending on competing requests. By

lowering the value of

filecache_max

, a larger amount of memory is available for other purposes,

without competing with ﬁle I/O requests.

What Are the Side Effects of Lowering the Values?

If there are many competing requests for physical memory, and the ﬁle cache tunables are set to too low a

value, very high demand on ﬁle I/O operations can eventually cause ﬁlesystem I/O performance degrada-

tion.

EXAMPLES

Set the ﬁle cache minimum to 10% of physical memory:

# kctune filecache_min=10%

Set a ﬁxed size ﬁle cache of 1 gigabyte:

# kctune filecache_min=1GB filecache_max=1GB

Set the ﬁle cache minimum to 15% of physical memory, and the maximum to 65% of the physical memory:

# kctune filecache_min=15% filecache_max=65%

WARNINGS

All HP-UX kernel tunable parameters are release speciﬁc. These parameters may be removed or have

their meaning changed in future releases of HP-UX.

Other tunable parameters related to sizing the buffer cache that existed in previous HP-UX releases are

now obsolete. The tunables

filecache_min

and filecache_max should be used to set limits to the

ﬁle cache. Note that, on any given system, the optimum values of these two new tunables are not neces-

sarily equivalent to the optimum values of the obsolete tunable values in the older systems. You should

ﬁrst determine if the new default values yield acceptable performance on your system, before attempting

to change the values of the new ﬁle cache tunables.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-

ter values. After installation, some tunable parameters may no longer be at the default or recommended

values. For information about the effects of installation on tunable values, 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

http://www.hp.com/go/hpux-core-docs

AUTHOR

filecache_max and filecache_min were developed by HP.