lotsfree_pct(5)lotsfree_pct(5)NAMElotsfree_pct - sets the upper bound before paging daemon starts steal‐
ing pages, specified as a percentage of available physical memory
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)