lotsfree_pct man page on HP-UX

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lotsfree_pct(5)						       lotsfree_pct(5)

       lotsfree_pct  - sets the upper bound before paging daemon starts steal‐
       ing pages, specified as a percentage of available physical memory

   Allowed values
       Must not be less than (see desfree_pct(5)).

       is a tunable parameter to set the upper bound before the paging	daemon
       starts  stealing	 pages.	  It  is specified as a percentage of physical
       memory available after boot.

       must be a positive integer between 0 and 30 and must  be	 equal	to  or
       greater	than  is  the lower bound before paging daemon starts stealing
       pages (see desfree_pct(5)).

       The paging daemon in HP-UX acts on a "two hand" model.  The daemon runs
       at  least once a second, with one part marking pages of virtual address
       space as "unused".  If the page is referenced before this "aging"  hand
       returns,	 it  will  be  marked as "used" again.	Another section of the
       daemon, the "steal" hand follows the age	 hand  (the  distance  between
       them  varies  in	 a  well  bounded range) and processes pages which are
       still marked unused, since needed or frequently	accessed  pages	 would
       have  a	high  likelihood  of  being  referenced in the gap between the

       Exactly how the steal hand treats the  pages  still  marked  as	unused
       depends on the comparison of free system physical memory and three pag‐
       ing parameters: and Between and is a  periodically  re-calculated  and,
       hence,  floating	 threshold  known  as Thus and are the upper and lower
       bounds between which moves.

       is an expression how much the system  maintains,	 in  percentage	 terms
       (percentage of physical memory available after boot).

       ·  If  is  greater  than	 the  system's	memory availability is in good
	  shape.  The steal hand does nothing as a  lot	 of  memory  is	 still
	  available  on the system, so there is no need to "steal" a page that
	  might be needed soon.

       ·  In the more common case, when is lower than  (but  higher  than  the
	  steal hand will begin to steal pages that have remained unreferenced
	  from when the age hand last marked them.  "Stealing" a  page	refers
	  to  the  process of freeing the page from being allocated for a par‐
	  ticular virtual page and making it available for general  allocation
	  again.  If falls below but still is more than memory availability is
	  still in reasonable shape, but the  paging  daemon  begins  stealing
	  pages	 more aggressively, including putting lower-priority processes
	  to sleep to free up their memory.

       ·  When is less than memory availability is getting more critical;  and
	  the  paging  daemon  begins  deactivating low-priority processes, in
	  other words, swapping out pages to the swap device.

       Since the exact memory topography varies widely across supported	 plat‐
       forms, these three boundary values are tunable to allow for cases where
       the default values are insufficient, or where the system	 administrator
       requires	 more  control over the actions of the paging daemon.  In gen‐
       eral, however, the automatic calculation performed  by  default	should
       suffice for most systems.  is a system calculated value.

   Who Is Expected to Change This Tunable?
       Anyone with super-user privileges.

   Restrictions on Changing
       Changes to this tunable take effect immediately.

   When Should the Value of This Tunable Be Raised?
       The  tunable  should  only be raised if an administrator feels that the
       current value provides insufficient free physical memory required by  a
       short  lived  but  critical process.  Increasing (and hence to an amout
       equal to or greater than the amount of physical memory required by this
       process	allows the swapper to move out less frequently used pages from
       longer running programs,	 increasing  the  probability  of  having  the
       desired	amount	of memory on hand without waiting for to drop below or
       during the execution of this critical process.

       Unless the current is set very low, raising for a process that  is  not
       short lived is fairly pointless as will almost certainly drop below and
       more likely even below thus waking up the swapper and allowing for  the
       physical	 memory	 to  be	 freed	up over the longer running time as the
       process requires it.

   What are the Side Effects of Raising the Value?
       The swap daemon will begin to steal less-frequently accessed pages from
       running	processes.   If	 large	amounts	 of physical memory is already
       available without the above situation, this will only slow the  already
       running	processes  if  they  need  to swap back in their stolen pages.
       Large amounts of free physical  memory  without	short-lived  processes
       that need it (as mentioned above) is simply a waste.

   When Should the Value of This Tunable Be Lowered?
       The  tunable  should  be lowered on systems where swapping is occurring
       that still have more physical memory available than is needed on	 aver‐
       age, and that have no sudden sharp peaks in memory usage.

   What are the Side Effects of Lowering the Value?
       System  swap  will  occur  at  a lower memory level.  If is set too low
       (keeping in mind that can never be greater than the system might	 stall
       due  to memory starvation upon new allocation even though swap space is
       available.  The stall would not be fatal, as the swap daemon run	 even‐
       tually, but will certainly hamper performance.

   What Other Tunable Values Should Be Changed at the Same Time?
       should  be  considered  when modifying since Attempting to set above is
       meaningless and will result in an error.

       Starting with HP-UX 11iv2, HP recommends the  use  of  to  specify  the
       upper bound for the paging daemon.

       Memory resource management infrastructure is busy.
		      Please try later.

       Attempting to set

       An invalid value is entered that is not an integer between
		      0 and 30, such as an negative number.

       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter may be removed or have its meaning changed in  future  releases  of

       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

       was developed by HP.


			   Tunable Kernel Parameters	       lotsfree_pct(5)

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