aio_proc_max(5) 						File Formats Manual						   aio_proc_max(5)

NAME

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

VALUES

   Failsafe
   Default
   Allowed values
   Recommended values
DESCRIPTION

       This  tunable  places  a  limit on the system resources that can be consumed 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 processes 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.	However, 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 without 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 rlimits 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 immediately 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 aio_reap(2).

   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 concern 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 tunable 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 (see

   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 memory 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)

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), 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)