system performance Post: 302442631

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Operating Systems HP-UX system performance Post 302442631 by poloUX on Thursday 5th of August 2010 03:01:51 AM

08-05-2010

Registered User

"also I need to understand the "pseudo-swap" i found this statement in book but don't understand "if we have 1 giga memory and 1 giga swap we can run 1.75 g processes "
ok if we don't have the pseudo-swap how much processe in this situation 1 G ? i am asking "

When a process is created, swap is checked too see if there is enough swap space for that process. The swap space is not actually allocated at that moment.
So, if you have 1 GB of RAM and 1 GB of swap space and you want to start a 1,5 GB process on a system that does not have pseudo-swap activated, you will not be able to start that process.
If you have pseudo-swap active, meaning 1 GB of swap space and [up to] 75% of 1 GB RAM results in 1,75 GB "virtual" swap space, you will be able to start that 1.5 GB process.
In HP-UX 11 v1 and v2 pseudo-swap is controlled by this kernel parameter: swapmem_on (1 is on). In 11.3, pseudo-swap is always enabled and swapmem_on parameter is no longer present.

hope it's more clear now the pseudo-swap space concept.

poloUX

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LEARN ABOUT HPUX

swapmem_on

swapmem_on(5)							     OBSOLETE							     swapmem_on(5)

NAME

       swapmem_on - OBSOLETE kernel tunable parameter

DESCRIPTION

       The tunable is obsolete.  Processes will always be allowed to use pseudo-swap space if it is available.

       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.

WARNINGS

       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.

							     Tunable Kernel Parameters						     swapmem_on(5)