aio_physmem_pct(5)						File Formats Manual						aio_physmem_pct(5)

NAME

       aio_physmem_pct - percentage of physical memory lockable for request call-back POSIX asynchronous I/O operations

VALUES

   Failsafe
   Default
   Allowed values
       The minimum value allowed is The maximum value allowed is

       Specify a positive integer value.

DESCRIPTION

       This  parameter places a limit on how much system memory can be locked by the total number of POSIX asynchronous I/O operations that are in
       progress at any given time.

       It is important to be aware that an operation remains on the active queue and memory is not released, even if the  operation  is  complete,
       until it is properly terminated by an call for that operation.

       The  value  of represents a percentage of system memory, and the limit it controls will adjust with Online Addition or Deletion of physical
       memory (OL*), as appropriate.

       Asynchronous I/O operations that use a request-and-callback mechanism for I/O must be able to lock the memory they are using.  The request-
       and-callback  mechanism	is  used  only	if  the  device  drivers  involved support it.	Memory is locked only while the I/O transfer is in
       progress.

       imposes a system-wide limit on lockable physical memory.  A per-process lockable-memory limit can also be self-imposed by using the  system
       call within the application program (see setrlimit(2)).

   Who Is Expected to Change This Tunable?
       System administrators that run applications requiring heavy usage of POSIX AIO to file systems.

   Restrictions on Changing
       This tunable is dynamic.  Any changes to the value of this tunable will take effect immediately without requiring system reboot.

       The amount of memory that can be locked under the limit imposed by cannot exceed the total system wide lockable memory limit imposed by

       The  limit  dictated  by  this  tunable,  is  checked  individually  for  each incoming request for file system or devices that support the
       request/callback mechanism.  When tuning to a lower value, the new limit will be immediately enforced for all new requests, and the  tuning
       will succeed even if the current usage count is higher.	The usage will then gradually adjust to the new limit.

   When Should the Value of This Tunable Be Raised?
       On a large server it is better to increase to higher values (up to 50).

   What Other Tunables Should Be Changed at the Same Time as This One?
       The total amount of memory that can be locked at any given time for any reason, not just for asynchronous I/O, is controlled by the system-
       wide limit Other system activity, including explicit memory locking with the and/or interfaces can also affect the amount of lockable  mem-
       ory at any given time.

       There  is no kernel parameter named but there is a parameter named that affects it.  The value of is determined by subtracting the value of
       from the amount of system memory available after system startup.  During startup, the system displays on the system console the	amount	of
       its lockable memory (along with available memory and physical memory).  These values can be retrieved while the system is running with com-
       mand.

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.

       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 values.  For information about the effects of installation  on  tun-
       able  values,  consult  the documentation for the kernel software being installed.  For information about optional kernel software that was
       factory installed on your system, see at

AUTHOR

       was developed by HP.

SEE ALSO

       kctune(1M), sam(1M), gettune(2), settune(2), aio(5), aio_return(2), dmesg(1M),  mlock(2),  plock(2),  getrlimit(2),  setrlimit(2),  unlock-
       able_mem(5).

							     Tunable Kernel Parameters						aio_physmem_pct(5)