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

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


 swapmem_on(5)                                                 swapmem_on(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      swapmem_on - allow physical memory size to exceed the available swap

 VALUES    [Toc]    [Back]
      1 (on)

    Default    [Toc]    [Back]
      1 (on)

    Allowed values    [Toc]    [Back]
      0 (off) or 1 (on)

 DESCRIPTION    [Toc]    [Back]
      In previous versions of HP-UX, system configuration required
      sufficient physical swap space for the maximum possible number of
      processes on the system.  This is because HP-UX reserves swap space
      for a process when it is created, to ensure that a running process
      never needs to be killed due to insufficient swap.

      This was difficult, however, for systems needing gigabytes of swap
      space with gigabytes of physical memory, and those with workloads
      where the entire load would always be in core.  This tunable was
      created to allow system swap space to be less than core memory.  To
      accomplish this, a portion of physical memory is set aside as
      'pseudo-swap' space.  While actual swap space is still available,
      processes still reserve all the swap they will need at fork or execute
      time from the physical device or file system swap.  Once this swap is
      completely used, new processes do not reserve swap, and each page
      which would have been swapped to the physical device or file system is
      instead locked in memory and counted as part of the pseudo-swap space.

    Who Is Expected to Change This Tunable?

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect on the next reboot.

    When Should the Tunable Be Turned On?
      If this tunable is set to 0 (off), and a fork() or exec() process is
      failing with an [ENOMEM] error message and has sufficient system
      memory but insufficient unreserved swap space, then setting this
      tunable to 1 (on) will allow these processes to use pseudo-swap space
      and execute.

    What Are the Side Effects of Turning the Tunable On?
      Some physical memory is set aside for pseudo-swap, but since the
      kernel can steal pages from this allocation if needed (for locked
      memory or kernel memory), and the rest of the pages will only be used

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

 swapmem_on(5)                                                 swapmem_on(5)
                          Tunable Kernel Parameters

      when physical swap is completely filled anyway, this is quite

    When Should the Tunable Be Turned Off?
      This tunable can be turned off if there are sufficient physical swap
      devices or file systems such that the system workload never fails to
      reserve swap.  However, turning this feature off really does not gain
      the system anything.

    What Are the Side Effects of Turning the Tunable Off?
      Processes will be limited to physical swap devices or file systems for
      reserving their swap on a fork() or an exec().

    What Other Tunables Should Be Changed at the Same Time?

 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]
      swapmem_on was developed by HP.

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
pmap_map FreeBSD map a physical memory range into kernel virtual address (KVA) space
dxsysinfo Tru64 Monitors system information such as CPU activity, memory, swap space, and file system usage
swchunk HP-UX swap chunk size in 1 KB blocks
swapctl IRIX manage swap space
swapctl Tru64 Manages the system swap space
addVirtualSwap IRIX adds virtual swap space
swapon HP-UX add swap space for interleaved paging/swapping
addLocalFileSwap IRIX adds swap space from a local filesystem
SwapManager IRIX view and manage system swap space
pvmove HP-UX move allocated physical extents from one LVM physical volume to other physical volumes
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service