Swap not being used?

wenberg · 07-27-2004, 12:57 AM

For some reason, my system isn't using any swap. It's been up for a month now and it hasn't used one kilobyte of swap once. The swap is initialized ... the system just doesn't use it. Any reasons why? And how I can fix this?

MS3FGX · 07-27-2004, 01:19 AM

Swap isn't generally used on modern systems. Only machines with very low RAM, or very high traffic ever use swap.

If your machine isn't using swap, that is a good thing. Your machine really shouldn't use any swap unless except in a rare instance.

I have always felt that any machine that needs swap regularly, is a machine that needs to be upgraded.

wenberg · 07-27-2004, 01:22 AM

The machine hasn't been using swap since I added a new hard disk on the last reboot. Before that though, it used swap fairly often ... though not aggresively.

MS3FGX · 07-27-2004, 01:25 AM

What is the output of:

Code:

free -m

and

Code:

swapon -s

wenberg · 07-27-2004, 02:29 AM

Output of ...

free -m

Code:

             total       used       free     shared    buffers     cached
Mem:           250        224         25          0         15        123
-/+ buffers/cache:         86        163
Swap:          462          0        462

swapon -s

Code:

Filename                                Type            Size    Used    Priority
/dev/hda2                               partition       473752  0       -1

MS3FGX · 07-27-2004, 03:03 AM

And you are saying that when the machine runs out of physical memory, swap isn't being used?

By the looks of that, you have a long way to go before swap would be needed. What was the system load like when you ran those commands?

wenberg · 07-27-2004, 11:56 AM

Yes, even when I have very very little system memory left, swap still does not kick in. One more thing, this didn't happen before upgrading to Slackware 10.0.

The system load when I ran those commands was relatively low ... but I have PHP scripts that use a lot of resources ... and swap still doesn't kick in when I run them.

J.W. · 07-27-2004, 01:30 PM

I agree completely with MS3FGX. Ideally, swap usage should be zero or as close to zero as possible. Using swap involves physical I/O to the hard drive, which as you know is several orders of magnitude slower than RAM, and therefore, the more swap is used, the worse the performance of your machine. If your swap usage is zero, I'd say that's a good thing, and something that you wouldn't want to change. -- J.W.

Cerbere · 07-28-2004, 01:22 AM

If you really want your box to use swap, you could take out some of your RAM (or switch to a smaller chip).

Or just start Gnome or KDE, that ought to chew up enough of your memory to need swap ;-)

Enjoy!
--- Cerbere