pseudo-swap question

[PamelaJThrasher]

When I run GlancePlus on one my 11.23 server, and look at the swap information by pressing 'w', it shows pseudo-swap with a priority of -1. What does this mean?

Pam

[spex]

Hi Pam,

From http://docs.hp.com/en/1218/mem_mgt.html#Pseudo-Swap%20Space:

Pseudo-Swap Space

System memory used for swap space is called pseudo-swap space. It allows users to execute processes in memory without allocating physical swap. Pseudo-swap is controlled by an operating-system parameter; by default, swapmem_on is set to 1, enabling pseudo-swap.

Typically, when the system executes a process, swap space is reserved for the entire process, in case it must be paged out. According to this model, to run one gigabyte of processes, the system would have to have one gigabyte of configured swap space. Although this protects the system from running out of swap space, disk space reserved for swap is under-utilized if minimal or no swapping occurs.

To avoid such waste of resources, HP-UX is configured to access up to 7/8 of system memory capacity as pseudo-swap. This means that system memory serves two functions: as process-execution space and as swap space. By using pseudo-swap space, a two-gigabyte memory system with two-gigabyte of swap can run up to 3.75 GB of processes. As before, if a process attempts to grow or be created beyond this extended threshold, it will fail.

When using pseudo-swap for swap, the pages are locked; as the amount of pseudo-swap increases, the amount of lockable memory decreases.

For factory-floor systems (such as controllers), which perform best when the entire application is resident in memory, pseudo-swap space can be used to enhance performance: you can either lock the application in memory or make sure the total number of processes created does not exceed 7/8 of system memory.

When the number of processes created approaches capacity, the system might exhibit thrashing and a decrease in system response time. If necessary, you can disable pseudo-swap space by setting the tunable parameter swapmem_on in /usr/conf/master.d/core-hpux to zero.

At the head of a doubly linked list of regions that have pseudo-swap allocated is a null terminated list called pswaplist.

Here's an excellent memory overview:

ftp://hprc.external.hp.com/memory.htm

PCS

[PamelaJThrasher]

Thanks so much for the all the information.
The one thing that I still do not understand is why pseudo-swap is showing in glance with a priority of minus one (-1). I thought the values could only be 1-10.

[spex · Accepted solution]

Hello,

Pseudo-swap is an exception to the rule. Assigning it priority of -1 forces it to be the first area to be used for paging.

Please remember to assign points to any responses you found useful.

PCS