Kernel (VM) swap problem in Hoary

[Paul M. Bucalo]

On Mon, 2005-06-06 at 10:44 +1000, Tim Long wrote:
> My experiences with smaller memory system:
> 
> I have been recently fiddling with a box with older AMD  350 MHz-128
> MB ram seeing if it is usable ubuntu. Installing kubuntu and reducing
> all the display settings to a minimal made the desktop very snappy and
> usable.

I've done the same in Gnome. It helps with minimum resources...

> With the default swappiness setting (60) open office is unusable. Once
> OO.org is loaded and the system stops thrashing the problem is that
> once you start entering or editing text the app will constantly pause
> for a second or two. If I set swappiness to 0 or 5 then the behaviour
> would stop so it appears that the default swappiness value is causing
> the system to keep trying to evict active OO.org memory pages to swap.

It does stop, but only until you open several heavy-weight apps and
leave them running. Eventually you just run out of RAM and the thrashing
begins again.

> I haven't tried high swappiness (90). It should make the situation worse (?)

Better, not worse. Go ahead and open OO, Mozilla Firefox, Evolution and
some other apps. Compose a lengthy email or post to this list, making
sure to take your time. It won't take long before your '0' or '5'
setting causes the system to be useless. Then change it to '90' and try
the same. You loose a little performance, but you won't be able to get
the system to go into a state of uselessness. The reason is that the
system is swapping smaller chunks more frequently instead of all at
once. I haven't been able to reproduce the uselessness state since
increasing it to 90.

> I have also discovered that the system has bigger problems with the
> cache/buffer settings. It seems to limit apps to 40-60 MB of RAM,
> anything above that seems to be dumped/held to swap. Caching RAM never
> seems to drop below 60 MB which is strange (commonly 70 MB+| of 126
> devoted to OS usage?). I can't seem to find any documentation on how
> to change this. Any ideas?

That's the problem, there isn't really any documentation that makes the
experimenting any easier. :0)

Paul