What is the swap for?

lydgate · 10-05-2005, 02:09 AM

Okay, so I have been trying to get suspend2 working on my laptop (eMachines m2352 running Slackware-current, kernel 2.6.13.3), and it panics. But during the process of setting this up, I realized that /dev/hda5, which was set as my swapspace, had never been activated with mkswap, because I was trying to suspend to my swapspace, and it wasn't letting me, saying there was 0 space there.

Anyway, so I ran mkswap /dev/hda5 and swapon /dev/hda5, but I noticed that no matter what I have running (as far as I can tell), top always indicates that 0k of swap is used. So what is it for, and if it's still not getting used, how can I fix this? Let me know what other information I should post.

shilo · 10-05-2005, 02:18 AM

Run more processes and you can get that swap used (compile a kernel, and open a bunch of X applications at the same time).

Swap is used when you run out of RAM.

It's a GOOD thing that your swap tends to stay at 0.

lydgate · 10-05-2005, 11:34 AM

I can't seem to open enough X programs to use any of the swap. It doesn't just tend to stay at 0, I've never even seen a kilobyte of it used, even when I have basically run out of ram . . . But I shouldn't worry about this?

KMcD · 10-05-2005, 11:51 AM

have you recompiled your kernel? Did you enable swap in the kernel config??

Vgui · 10-05-2005, 02:11 PM

How much RAM do you have? If you have a bunch (ie: 1gb+) it is likely that you won't touch swap, unless you open every application you own. I stopped putting swap on my machines once I hit 1gb of RAM, even a 512mb system doesn't tend to use swap.

Tinkster · 10-05-2005, 02:50 PM

True: my new toy here at work has 16GB and I haven't
seen it swap yet ... :D

Cheers,
Tink

raska · 10-05-2005, 04:27 PM

nice *toy* you got Tinkster! lol

In the office's computer I have got 784 mb in RAM, it starts to swap when I use a winxp virtual machine which I have for office purposes, though my laptop has 512 RAM and it never swaps even when I'm playing UT2004

kencaz · 10-05-2005, 04:37 PM

Yeah! I think the SWAP partition is becoming less and less needed nowaday's with all the ram available for processes... I still add a half Gig swap to all my particians anyway... Never tried to install a disto with no SWAP partition... I guess it would not matter but don't really know if it is really needed during the install.

KC

Tinkster · 10-05-2005, 05:05 PM

Quote:

nice *toy* you got Tinkster! lol :D

In the office's computer I have got 784 mb in RAM, it starts to swap when I use a winxp virtual machine which I have for office purposes, though my laptop has 512 RAM and it never swaps even when I'm playing UT2004

Well, I'm certain that once Oracle is up and running on
it I *will* see swapping.

Cheers,
Tink

yuchai · 10-05-2005, 05:11 PM

I've seen swap used when running VMWare. Anyhow with the price per GB of hard drives these days, might as well use a 1GB or so swap partition for peace of mind. What's that..like 60 cents USD?

raska · 10-05-2005, 05:24 PM

Quote:

Originally posted by Tinkster
Well, I'm certain that once Oracle is up and running on
it I *will* see swapping.

Cheers,
Tink

maybe not even with an Oracle instance running lol

we have in the office a SAP / Oracle system with 4 GB RAM (11 GB of swap configured) in unix solaris with around 100 active users and never swaps a bit

lydgate · 10-05-2005, 06:02 PM

I have 512 RAM, it's a laptop, I'm not doing anything super intensive but I was just wondering whether it should be getting used at all. Yes, I have recompiled my kernel, I will check in there to see if I disabled it somehow, where exactly is the option?

shilo · 10-05-2005, 06:30 PM

This is all, I believe

Code:

shilo@shilo2:~$ cat /boot/config-2.6.13.2 |grep -i swap
CONFIG_SWAP=y
CONFIG_X86_BSWAP=y

lydgate · 10-05-2005, 11:37 PM

I get

Code:

CONFIG_SWAP=y
CONFIG_X86_BSWAP=y

along with a few suspend2 things

so i guess i just have enough ram to open a bunch of X apps

shilo · 10-06-2005, 01:57 AM

If you really want to see your swap get used, fire up one of the big-dog DEs (KDE/Gnome). Then, install azureus (that seems to use up memory REALLY well

(300+MB well, sometimes)). Fire up a couple terminal emulators, a few web browsers (firefox is good for 100+MB), and start browsing. Shouldn't take too long.

I run Azureus, Gnome, Firefox (lots of tabs), Evolution, gnome-terminal, and rhythmbox all at once pretty frequently. With 512MB ram, I can just start swapping a little.