Grant wrote:
...
To confuse you even more, there is a swappiness setting as well. On my old
x86 rig, I have 2Gbs of ram. My hard drive is really slow since it is IDE.
I set swappiness to 20. That tells the kernel that I have swap space but
don't use it unless you must. For what I use the rig for, 2Gbs is plenty of
ram. The lower the swappiness setting, the less the kernel will try to use
ram. The higher the setting, the more it will try to use swap.
I have a new rig that is amd64 and has SATA drives which are pretty fast. I
still have swappiness set to 20. Why do I have it set to 20 when the drives
are faster you ask? I have it set to 20 because I have 16Gbs of ram here.
Even if I have portage's work directory on tmpfs and am compiling OOo, it
should not need swap then either.
By the way, my swap partition is 1Gb on both systems. Why have it this way
since one machine has 2Gbs and one has 16Gbs? As it has been said, you want
a little swap and even using a little swap is OK. You just don't want it to
be using swap and actually swapping data all the time. On my old rig, it
started out with 512Mbs. I use KDE and it got to the point where it was
using enough ram that it was not just using swap and letting things sit, it
was actively swapping data from swap and doing so a lot. It would only be
using a 100Mbs sometimes 200Mbs. The point is, it was slowing the system
down because of the swapping process. I bought a stick of ram and all was
well again. It would still use a 100Mbs of swap at times but it would not
be actively swapping the data back and forth so it wasn't a big deal.
I think the point is this, it is good to have a little swap. It is even OK
for it to use a little swap when it is mostly sitting there. When you
notice it using swap and it is actively swapping and moving things back and
forth, you need more memory. Having the swap may can save you from a crash
but is can also give you a "time to add more ram" hint too. If Linux starts
using swap a good bit, you need more ram.
OK, how can you determine when a machine is actively swapping and
moving things back and forth? Do you need to monitor the system with
a real-time tool during peak usage?
- Grant
I use gkrellm on mine. It has a little charty thingy. I think iotop
will show if anything is being swapped to. There may be others as well
for a console or non-X machine. Most people know of top but that really
doesn't help a lot. It doesn't show things moving just how much is
being used. I think there is a better command that shows this but dang
if I can recall it right now. Somebody help a old fart out here. lol
Dale
:-) :-)
