stupid question about shmmax, shmmni and shmall...

[Giacomo Mulas <gmulas@oa-cagliari.inaf.it>]

Hello, I am trying to run a demanding quantum chemistry program on a cluster
of multiprocessor machines.  Each machine has 2 dual-core opterons and 16Gb
of RAM, and is running a 64 bit kernel (currently 2.6.26) and userspace
(lenny) system.  Interprocess communications among processes on the same
node go via shared memory (a lot of it), hence I need to set it to the
maximum possible.

Can somebody tell me what are the maximum supported values for shmmax,
shmmni and shmall (I know I can set them via /proc/sys/kernel pseudofiles)
or (even better!) tell me how I can calculate them?  Is it likely that a
too large value of shmmax or the other two can cause applications to
segfault?

Thanks in advance,
Giacomo Mulas

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Giacomo Mulas <gmulas@ca.astro.it>
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