Computer behaving oddly

[taimatsu]

Computer is being annoying and I cannot pin down why. Suggestions and advice welcome. (Reminder: this machine runs Debian Etch/KDE.)

Basically, it's mostly fine, except that sometimes it runs very slowly. When it does this, the 'hard disk activity' LED lights constantly, and I can hear "chug chug chug chug.... chug chug chug chug..." noises from it. I can't see anything using 'ps wux' which would indicate what was causing this. However, by trial and error, it seems to be something to do with my iceweasel browser. I have no idea what, and it's not as straightforward as 'iceweasel runs, thigns break', but once I start opening several tabs and doing other stuff - which the machine coped fine with a few weeks ago - things start moving at a snail's pace and the computer becomes almost unusably slow. How do I work it out? It's driving me nuts.

Comments

[diffrentcolours]

At a guess, it's something to do with your computer running out of memory, and hence having to use the hard drive as "swap", basically as extra memory, which is much slower. You can tell how much memory your computer is using (in megabytes) with free -m; the output on my system is:

             total       used       free     shared    buffers     cached
Mem:           512        506          5          0         72        153
-/+ buffers/cache:        280        231
Swap:         1023          0       1023

Note that there is 0 swap used on my system, and I've actually got 231Mb of RAM free (the kernel likes to steal any spare real memory for cacheing to speed your system up, but will stop doing that if it's needed for real stuff). One other thing you can do is run top which shows the top processes by CPU usage, then press M (note the capital letter) to see this by memory usage instead. There's probably some GUI tool to do all this but I don't know what it is :)

Using swap shouldn't make your system unusable, unless something's happening which is causing your system to "thrash" (constantly loading stuff in and out of swap). If the problem is related to web browsing, could it be related to the websites you're viewing? Lots of Flash sites are pretty crappy at memory usage, and you might find helpful an extension like Flashblock which only loads the Flash you want.

Another cause of your slowdown might be a dodgy hard disk; the first thing you can do is run hdparm -d /dev/hda which should give output like this:

/dev/hda:
 using_dma    =  1 (on)

This tells you that your system is using Direct Memory Addressing, a much faster way of talking to hard drives. If it isn't, you can enable it with hdparm -d 1 /dev/hda.

It's probably worth checking whether your hard drive is reporting any failures itself, but I don't have time to write that up right now; see if the above gets you anywhere and make sure you have backups!