aio_physmem_pct man page on HP-UX

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aio_physmem_pct(5)					    aio_physmem_pct(5)

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

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

       Specify a positive integer value.

       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 mem‐
       ory (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 sup‐
       port 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 can‐
       not 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 memory 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.  Dur‐
       ing 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 command.

       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.

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

			   Tunable Kernel Parameters	    aio_physmem_pct(5)

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