aio_proc_max man page on HP-UX

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aio_proc_max(5)						       aio_proc_max(5)

       aio_proc_max  -	maximum	 number	 of  async  I/O operations that can be
       queued by any process that uses aio_reap()

   Allowed values
   Recommended values
       This tunable places a limit on the system resources that	 can  be  con‐
       sumed  by  processes  that use aio_reap(2).  The limit is enforced at a
       per-process level to improve scalability as the number of CPUs and pro‐
       cesses increases.

       When  this  tunable  is	set to 0, it has no effect.  That is, resource
       usage will be restricted by the other limits provided on HP-UX.	(These
       include	and setrlimit(2) with Use of these limits (while keeping at 0)
       ensures compatibility with POSIX standards and legacy applications.

       However, most of these other limits are	enforced  at  the  system-wide
       level,  and  they  can in some cases reduce scalability.	 To solve this
       problem when compatibility with the other limits is not	required,  the
       tunable can be set.

       When  is	 set  to  a  positive value, it becomes the only tunable limit
       enforced for processes that use aio_reap(2).  Memory-usage limits (e.g.
       or  will	 NOT  be enforced for aio_reap(2) processes when is set.  How‐
       ever, processes that use POSIX AIO without aio_reap(2) (i.e. only using
       standard	 POSIX	interface  calls) will continue to have all of the old
       limits enforced.

       For sysadmins wishing to obtain the increased  scalability  of  without
       giving  up control of memory limits, the tunable can be set.  That tun‐
       able limits the size of each I/O, effectively  constraining  the	 total
       memory usage of all processes that use aio_reap(2) by the quantity:

       This approach provides full control of system-wide resource usage with‐
       out depending on explicit system-wide constraints.

       Note: when is  set,  processes  that  use  aio_reap(2)  can  still  set
       process-specific limits with the limit.	The minimum of and will be the
       value that is enforced by the AIO subsystem.  However, ALL other	 rlim‐
       its  related to AIO will have no effect (i.e. will not be enforced) for
       aio_reap(2) users when is non-zero.

   Who Is Expected to Change This Tunable?
       System administrators that run applications requiring  heavy  usage  of
       AIO (with aio_reap(2)) to disks or filesystems.

   Restrictions on Changing
       This  tunable is dynamic.  Changes to to this tunable take effect imme‐
       diately for new processes started after the change.  But	 they  do  not
       impact  existing	 running  processes.  (That is, any process running at
       the time of tuning will be "grandfathered" in, and will adhere  to  the
       value held by this tunable at the time the process was started)

   When Should the Value of This Tunable Be Raised?
       should  be  raised  for	applications that make heavy usage of AIO with

   What Are the Side Effects of Raising the Value of This Tunable?
       When raising this tunable from its default of 0 to  a  positive	value,
       the  effects  described above will take place.  (see However, once this
       tunable is a positive value, the only effect of raising it  further  is
       that more system resources can be used for asynchronous I/Os.

   When Should the Value of This Tunable Be Lowered?
       should  be lowered when AIO performance is acceptable but there is con‐
       cern about too many system resources being devoted to AIO.

   What Are the Side Effects of Lowering the Value of This Tunable?
       As long as it remains a positive value, lowering the value of this tun‐
       able  simply  decreases the number of I/Os that each process can issue.
       When this tunable is set to 0, it will cease to have an effect, and the
       system  will  enforce only the old system-wide tunables described above

   What Other Tunables Should Be Changed at the Same Time as This One?
       No additional tunables need to be changed at the same time as this one.

       However, can optionally be set if there is an interest in limiting mem‐
       ory usage for AIO.

       In  addition,  when  is	set  to a positive value, another option is to
       lower the values of the older system wide limits (such as and  This  is
       useful  because	the  older  limits  will have no impact on aio_reap(2)
       users, and aio_reap(2) users are expected to consume  the  majority  of
       system  resources.   (Leaving  less resources for processes governed by
       the older limits)

       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), aio_reap(2), gettune(2), settune(2), setrlimit(2),
       aio(5), aio_iosize_max(5).  aio_max_ops(5), aio_physmem_pct(5).

			   Tunable Kernel Parameters	       aio_proc_max(5)

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