hi,
I saw some threads discussing how to clear the disk cache, but is it possible to configure the system not to use disk cache at all? How is that done?
Thanks.

I believe the command you are looking for is sdparm.

Be warned though its a very powerfull command and must be used with care, read the documentation fully before using.

Thanks Jonathan.

If I'm not mistaken this command addresses only SCSI devices. I am looking for a way to configure the system not to use cache at all (e.g. set the cache size to 0) that will work whatever memory I'm using (e.g. USB, RAM only).

Thats correct (although linux seems to denote all disks as scsi now, even if technically some should be hd*) so using sdparm should disable the write cache of the drives.

The following link, and its referenced links, may provide some insight to linux kernel cache as thats way beyond my knowledge.

http://www.westnet.com/~gsmith/conte...ux-pdflush.htm

No (presuming you are talking about the page-cache).

Questions such as this generally indicate an insistence on a perceived answer - usually an incorrect one.
What is the problem you are trying to solve ? - the problem, not symptoms.

Thank you Jonathan. Thank you Syg00.

I am working on an embedded system that has no disk of its own, but may have USB inserted. so there are two problems I'm looking for answers:
1. I'm not sure what is the actual meaning of swapping when there is no disk at all
2. I want to test how much RAM I actually need for operation.
these two issues lead me to disabling the cache - at least for testing.

Linux will work fine without swap at all - so long as you have sufficient memory (RAM). Swap is merely "overflow" for RAM.
Page-cache (what you see as cached in "free") is merely a convenient use for otherwise unused RAM. If otherwise needed (by userland applications) the page-cache is released. Automagically.
I suspect you are worrying unnecessarily.

Calculating how much memory your processes need is more "black art" than science. Even the kernel devs haven't pinned that one down satisfactorily. I'll get back to you with some suggestions - presuming you have a full set of tools available (/proc, /sys, perl ... that sort of thing).

Thank you very much. Looking forward for any "black art" suggestions :-)

Rather than re-hash the old threads about how to account memory, go get ps_mem.py
Works the way I generally think it should, and the imbedded comments are informative background - as well as the python code itself of course.

I will dig into this script.
Thank you.