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

2009-03-05 Thread Basile STARYNKEVITCH 

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

2009-03-05 Thread Ron Peterson 
I bookmarked a fairly decent description of these parameters a while
back:

http://www.puschitz.com/TuningLinuxForOracle.shtml#SettingSharedMemory

Maybe you already know this, but you can also set these parameters in
/etc/sysctl.conf.  That way they persist between reboots, etc.

-Ron-

2009-03-05_13:43:30-0500 Giacomo Mulas :
> 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
> 
> -- 
> _
> 
> Giacomo Mulas 
> _
> 
> OSSERVATORIO ASTRONOMICO DI CAGLIARI
> Str. 54, Loc. Poggio dei Pini * 09012 Capoterra (CA)
> 
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> Tel. (UNICA): +39 070 675 4916
> _
> 
> "When the storms are raging around you, stay right where you are"
>  (Freddy Mercury)
> _
> 
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stupid question about shmmax, shmmni and shmall...

2009-03-05 Thread Giacomo Mulas 

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

--
_

Giacomo Mulas 
_

OSSERVATORIO ASTRONOMICO DI CAGLIARI
Str. 54, Loc. Poggio dei Pini * 09012 Capoterra (CA)

Tel. (OAC): +39 070 71180 248 Fax : +39 070 71180 222
Tel. (UNICA): +39 070 675 4916
_

"When the storms are raging around you, stay right where you are"
 (Freddy Mercury)
_

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