Miniscule SHMMAX causing trouble

John Goerzen (jgoerzen@complete.org)
Sat, 9 Jan 1999 18:54:13 -0600

I have been trying out the "buffer" program. This thing can make use of a
lot of shared memory. Unfortunately, it was not working for me. Martin
Buck, the Debian developer that I wrote to about it, pointed this out:

wallace:$ grep '#define SHMMAX' /usr/local/src/linux-2.0.34/include/asm-alpha/shmparam.h
#define SHMMAX 0x3fa000 /* max shared seg size (bytes) */
^^^^^^^^
whereas:

wallace:~$ grep '#define SHMMAX' /usr/local/src/linux-2.0.34/include/asm-i386/shmparam.h
#define SHMMAX 0x2000000 /* max shared seg size (bytes) */
^^^^^^^^^

Now, I am indeed on Alpha. Why is the maximum shared memory size on Alpha
miniscule like that? Certainly a 64-bit machine should be able to use at
least as much shared memory as a 32-bit one!

Is this something that I can tweak and set to an arbitrary value?

This problem is in all the way from 2.0.x to 2.2.0pre.

Thanks,
John

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