filecache_max man page on HP-UX

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filecache_max(5)					      filecache_max(5)

       filecache_max,  filecache_min  -	 maximum or minimum amount of physical
       memory used for caching file I/O data

       The defaults are computed and  adjusted	automatically,	based  on  the
       amount physical memory on the system.

       The  current  default value, when displayed by will be expressed as the
       current value used internally by the system (representing bytes).   The
       displayed  value	 will  vary  as	 the  internal	value is automatically

   Allowed values
       not less than the equivalent of 1 megabyte

       not less than the equivalent of 1 megabyte

       not greater than the equivalent of 70% of physical memory

       not greater than the equivalent of 90% of physical memory

       See below.

       Values can be specified as:

	      1) Default

	      2) A percentage of total physical memory:
		     A positive whole number followed by a percent symbol (for
		     example, 70%).

	      3) A constant value:
		     A	positive  whole number that represents number of bytes
		     of physical memory, optionally followed by	 a  multiplier
		     suffix, where and

   Recommended values
       It  is  recommended  that  these	 tunables  are	left  in the automatic
       (default) state, to allow the system to better balance the memory usage
       among filesystem I/O-intensive processes and other types of processes.

       These  tunables	control the amount of physical memory that can be used
       for caching file data during file system I/O operations.

       The amount of physical memory that  is  specified  by  the  tunable  is
       reserved and guaranteed to be available for file caching.

       The  amount of physical memory used for file caching can grow beyond up
       to depending on I/O load and competing requests for physical memory.

       When these tunables are set to default, or set to a percent value, they
       automatically adjust with Online Addition or Deletion (OL*) of physical
       memory, as appropriate.

   Who Is Expected to Change These Tunables?
       The automatic (default) state should be appropriate for	most  environ‐

       You  must  set  these tunables to a constant value (not default or per‐
       cent) if you want to specify file cache limits with  finer  granularity
       than  percent  of physical memory (for example, a minimum size or fixed
       size of <1% of physical memory).

       You must set these tunables to a constant value (not  default  or  per‐
       cent)  if  you  do not want the limits of the file cache to adjust with
       OL* of physical memory.

       To discriminate in favor of deterministic I/O  on  systems  with	 large
       file I/O activity, or on the contrary, to discriminate in favor of bet‐
       ter performance of non-I/O-intensive processes, you can consider chang‐
       ing  the	 values of these tunables, keeping in mind the side effects as
       described below.

       To determine a reasonable value for the cache size you should  consider
       the  file  I/O-intensive	 applications  on your system, and the size of
       their working set.  Depending on the type of applications, the  working
       set  size  can  be  based on the size of a transaction, or data size in
       given unit of time.  For	 example,  for	a  conservative	 value	of  in
       megabytes, you can use the following formula:


       Only those processes that actively use disk I/O for file data should be
       included in the calculation.  All others can  be	 excluded.   Here  are
       some  examples of what processes should be included in or excluded from
       the calculation.

	      NFS daemons, text formatters, database management	 applications,
	      text  editors,  compilers,  and so on, that access or use source
	      and/or output files stored in one or more file  systems  mounted
	      on the system.

	      X-display applications, login shells, system daemons, or connec‐
	      tions, and so on.	 These processes use very little, if any, disk
	      I/O for file data.

   Restrictions on Changing
       These tunables are dynamic and automatic.

       The  system  rounds  the specified tunable value(s) down to the closest
       physical page boundary.

       The amount of physical memory represented by must be equal to  or  less
       than the memory represented by tunable

       Setting these tunables to a constant value will de-couple them from OL*

       Tuning up of the parameter may fail if there is not enough free	physi‐
       cal memory to satisfy the request.

       These  tunables,	 and  must  both  be  set  to a relative state (either
       default of percent state), or must both be set  to  a  constant	value.
       For example, the following are acceptable settings:

       The following will result in an error:

       If is currently set to default, the following is acceptable:

       But the following will result in an error:

       See other restrictions in the section above.

   When Should the Value of These Tunables Be Raised?
       Low  system  performance at initialization time and/or on a system with
       filesystem I/O-intensive processes may be an indication that the values
       of these tunables are too low.  If there is a large number of processes
       actively and constantly using file data I/O, you should raise the value
       of for more deterministic I/O.  In most cases, especially when the file
       data I/O is expected to peak only occasionally, it is recommended  that
       the value of the maximum limit, is raised instead.

   What Are the Side Effects of Raising the Values?
       The amount of memory reserved for the minimum file cache size, dictated
       by 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, can be lowered to allow a  larger  per‐
       centage	of  memory  to	be used for purposes other than filesystem I/O
       caching, depending on competing requests.  By lowering the value	 of  a
       larger  amount  of memory is available for other purposes, without com‐
       peting 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 degradation.

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

       Set a fixed size file cache of 1 gigabyte:

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

       All HP-UX kernel tunable parameters are release specific.  These param‐
       eters 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  and
       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 nec‐
       essarily	 equivalent to the optimum values of the obsolete tunable val‐
       ues 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 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 at

       and were developed by HP.

       kctune(1M), sam(1M), gettune(2), settune(2).

			   Tunable Kernel Parameters	      filecache_max(5)

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