*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->HP-UX 11i man pages -> aio_physmem_pct (5)              


 aio_physmem_pct(5)                                       aio_physmem_pct(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      aio_physmem_pct - percentage of physical memory lockable for request
      call-back POSIX asynchronous I/O operations

 VALUES    [Toc]    [Back]

    Default    [Toc]    [Back]

    Allowed values    [Toc]    [Back]
      The minimum value allowed is 5.  The maximum value allowed is 50.

      Specify a positive integer value.

 DESCRIPTION    [Toc]    [Back]
      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
      aio_return() call for that operation.

      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 requestand-callback
 mechanism is used only if the device drivers involved
      support it.  Memory is locked only while the I/O transfer is in

      aio_physmem_pct imposes a system-wide limit on lockable physical
      memory.  A per-process lockable-memory limit can also be self-imposed
      by using the setrlimit() 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    [Toc]    [Back]
      This tunable is static.  Any changes to the value of this tunable will
      require system reboot before taking effect.

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

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

 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004

 aio_physmem_pct(5)                                       aio_physmem_pct(5)
                          Tunable Kernel Parameters

    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 lockable_mem.  Other system activity, including
      explicit memory locking with the plock() and/or mlock() interfaces can
      also affect the amount of lockable memory at any given time.

      There is no kernel parameter named lockable_mem, but there is a
      parameter named unlockable_mem that affects it.  The value of
      lockable_mem is determined by subtracting the value of unlockable_mem
      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 /sbin/dmesg command.

 WARNINGS    [Toc]    [Back]
      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 tunable
      values, consult the documentation for the kernel software being
      installed. For information about optional kernel software that was
      factory installed on your system, see HP-UX Release Notes at

 AUTHOR    [Toc]    [Back]
      aio_physmem_pct was developed by HP.

 SEE ALSO    [Toc]    [Back]
      kctune(1M), sam(1M), gettune(2), settune(2), aio(5), aio_return(2),
      dmesg(1M), mlock(2), plock(2), getrlimit(2), setrlimit(2),

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
dbc_max_pct HP-UX maximum percentage of memory to be used for caching file I/O data and metadata
dbc_min_pct HP-UX minimum percentage of memory used for caching file I/O data and metadata
pvmove HP-UX move allocated physical extents from one LVM physical volume to other physical volumes
mem Tru64 physical memory interface
msync IRIX synchronize memory with physical storage
pmap_copy FreeBSD copy physical memory pages
pmap_copy_page FreeBSD copy physical memory pages
mlock FreeBSD lock (unlock) physical pages in memory
munlock NetBSD lock (unlock) physical pages in memory
munlock FreeBSD lock (unlock) physical pages in memory
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service