Re: Need assistance in determining memory usage

[Dan Kegel]

  Thomas Schenk <[e-mail]> wrote:
 > We are building an online game system.  On some of
 > the systems, there are simulator processes running
 > that each service a player.  There may be up to
 > 200 or more of these processes running at any given
 > time and each uses a fairly large amount of memory
 > ...  When the simulator processes start swapping,
 > the systems are becoming unstable, performance goes
 > all to hell...  It would
 > be useful for us to be able to monitor as closely as
 > possible the amount of memory each processes is using
 > and especially to be notified when these processes
 > start using significant amounts of swap, so that we
 > can be prepared to react before the situation gets
 > out of hand.  The other reason why we want to collect
 > this data is so that the developers can analyze the
 > process when it starts to swap ...

A few things you might try:

1. Set RLIMIT_DATA or RLIMIT_AS for your processes
using ulimit.  That should cause malloc() and the
like to return NULL or throw an exception if you go
over the limit.  (RLIMIT_AS doesn't work too well
on heavily multithreaded programs, though, because
of the many stacks.)

2. Try the no-overcommit patch.  That will fail
allocation requests that might conceivably cause swapping
later.  Harsh, but you did want early notification :-)

3. Start reading the kernel source to see how it calculates
memory use and enforces the above limits.  That helped
clarify things for me a bit.

4. If you're feeling really nasty, you could try applying
my patch that implements RLIMIT_RSS by killing the process.
That's pretty immediate feedback, too :-)

- Dan