Re: stupid question about shmmax, shmmni and shmall...

[Basile STARYNKEVITCH <basile@starynkevitch.net>]

Giacomo Mulas wrote:
> 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. 


The shared memory IPC could also be done thru mmap calls with 
appropriate parameters (a real common open file descriptor, MAP_SHARED, 
....)
I believe you won't have real size limitation but I would suggest to 
have the mmap-ing fit into RAM.

Of course, you have to synchronize your processes using some different 
mechanism (pipes, sockets, IPC semaphores semget & semop, Posix 
semaphores, ...) or even maybe mutex inside the common shared mmap-ed 
memory

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Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
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