topic Re: pagefile Reservable issue in Operating System - OpenVMS

pagefile Reservable issue

skynet1980 — Mon, 29 May 2006 03:19:19 GMT

Hi ,
I used show mem check my vax resouce and found that :
Paging File Usage(pages): Free Total
DISK$SPNVX1:[SYS1.SYSEXE]SWAPFILE.SYS 60000 60000 60000
DISK$SPNVX1:[SYS1.SYSEXE]PAGEFILE.SYS Reservable 102400 -7220 102400

pagefile's Reservable value is negative , is it normal or abnormal ?

Re: pagefile Reservable issue

Wim Van den Wyngaert — Mon, 29 May 2006 03:23:31 GMT

It is normal. VMS promised processes more memory than they took. If they all take it, your pagefile is full.

Wim

Re: pagefile Reservable issue

Ian Miller. — Mon, 29 May 2006 16:45:00 GMT

I guess this is a version of VMS before V7.3?

It is not usual to see a negative reservable figure. Process will reserve pages 2000 pages at a time (depends on a system parameter). Each process may not use all the pages it reserved.
Your system will probably be ok as long as there is plenty of memory on the free list. Once processes start trying to use the pagefile they have reserved the system will run out and hang.

Consider it a warning and if you can increase the pagefile by 20%.

Re: pagefile Reservable issue

John Gillings — Mon, 29 May 2006 20:44:38 GMT

A negative reservable means "this is how much extra pagefile you would have needed if you were running Unix or Windows" :-)

As long as you have sufficient FREE space (rough rule of thumb >50% or at least 200,000 blocks) then a negative reservable is an indication of the efficiency of the paging algorithm.

In your case, total and free are equal, so although you've overallocated your pagefile, you're not actually using *any*. No processes on your system have any interest in the swap file either. Translation - everything is running in memory, which is generally a good thing.

In absolute values, your 50MB of pagefile is really quite small. You may want to consider increasing it, BUT since you're not using it, there's no compelling reason to increase. Just keep an eye on the free space. If it ever goes below 50000 reevaluate the allocation.

Re: pagefile Reservable issue

comarow — Tue, 30 May 2006 08:02:08 GMT

I believe that many years ago, when a process was created, the pagefile quota
was actually allocated in the pagefile.

Reservable memory was a holdover, with little meaning. Thus, if every process used all their pagefile quota, that was the
reservable memory field. In reality, it's interesting, but meaningless.