SUMMARY: What happens when shmmax is set above MAXINT on 2.6?

From: Cain, Allen <>
Date: Wed Jan 22 2003 - 13:19:50 EST
Many thanks to Casper Dik, Rich Teer, and especially Michael Schulte for
reminding me of some simple arithmetic.

My question (paraphrased):

My group has an E6500 server running Solaris 2.6 with the shmmax kernel
parameter set to 6 GB.  The system boots and is running just fine; however,
sysdef reports that shmmax is set to 2GB.  I wanted to know if this would /
could cause problems other than performance degradation, and I also was
curious as to how the OS arrived at 2GB.

Basic answers:

Shouldn't be an issue with the system (and we'll fix it next time we get a
chance).  With regards to the 2 GB value, the system apparently chopped off
the high-order bit.  6 GB = 2^32 + 2^31, after shifting the high-order bit
you get 2^31 = 2 GB.  I knew I was missing something simple.

Thanks once again!

Allen Cain    MP 5H - C
System Administrator
IS / Application Server Engineering
Tennessee Valley Authority
sunmanagers mailing list
Received on Wed Jan 22 13:26:36 2003

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