[Sheflug] memory usage in linux

["David Willington" <david.willington@xxxxxxxxxxxx>]

Dear All

Can anyone point me at a comprehensive explanation of memory usage? I'm
managing a LAMP server (running moodle and a content management system) on
Fedora Core 5. It has 3 Gb RAM, 2GB Swap (which I suspect is too small)
and I forget the processor. We're testing how it handles simultaneous
logons to moodle and I'm trying to make sense of the outputs of top and
ps, how best to tweak apache and mysql configuration values (eg the
maximum number of apache clients, keepalive (whether on or off is best for
us), how long connections are kept if keepalive is on etc). We know that
if 4 classes (110 users or thereabouts) try to log on simultaneously the
server crashes whereas a class of 30 or so can log on simultaneously,
albeit painfully slowly at the moment, although once they're on
everything's fine. To complicate things a bit more, authentication is
carried out against the schools Active Directory server, so I don't know
if this is contributing to slowing things down and perhaps having an
impact on memory usage as processes are taking longer than they need to.

I'm not in front of the machine at the moment so I can't cut and paste
output, but without anyone logged on the output of top shows 2Gb memory
being used, and that's without a graphical interface. I hope the problem
is that I don't understand how to interpret the figures I see, which is
why I'm trying to find a comprehensive explanation of how memory works and
how I interpret these figures.

Thanks

David


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