... > 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
