Kernel (VM) swap problem in Hoary

[Tim Long]

> > 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...

Do you have an idea how to reduce the eye-candy/memory usage for
gnome? KDE has a large(ish) number of control panel settings that can
turn things off. Gnome doesn't appear to have the same customization
abilities built in.

> > 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.

That is something I need to try. I'm currently thinking out a
framework for recording swap file usage and graphing. I've just
noticed that the SI and SO fields in vmstat are broken (return a value
of 0 all the time) which makes life more difficult.

> > 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)
> 

I am thinking that maybe the disk IO scheduler is consuming/reserving
a large amount of  memory. I hope to try changing from the
anticipatory scheduler to maybe dead line and see if this helps.

Tim.