From: Chris Bryant (Chris.Bryant@DTAG.Com)
Date: Wed Mar 05 2003 - 10:19:29 EST
Thanks to Alan Rollow - Dr. File System's Home for Wayward Inodes.
[alan@desdra.cxo.cpqcorp.net], Dr. Thomas Blinn, and Peter Gergen for their
responses. Here are their responses
Alan Rollow -
The shared memory is virtual memory. It can be paged, just
like all other virtual memory. And, OSF/1 (*) being lazy
about allocating pages to virtual memory, if it hasn't ever
been touched, it may not have ever had pages allocated to it.
I don't know that this is the case, but seems the most
plausible to me.
(*) OSF/1 -> DEC OSF/1 -> Digital UNIX -> Tru64 UNIX
Dr. Thomas Blinn -
Are you assuming that shared memory is "wired" (can't be paged in and out)?
That's not so.. it is demand paged like process private memory unless you
programmatically lock it into physical memory, and doing so is messy with
shared memory segments because you would also have to explicitly release it
when all the applications exit, unless you want to tie up physical memory.
This whole thing is probably not broken, so you might be well advised to not
try to "fix it".
Peter Gergen -
Sounds like there is an inclusion of your swap space in the calculation for
virtual memory.
I am gathering from these responses that it can be paged so my vmstat -P
still is correct with regards to virtual memory being used.
Chris
-----Original Message-----
From: Chris Bryant
Sent: Tuesday, March 04, 2003 11:10 AM
To: Tru64 Unix (tru64-unix-managers@ornl.gov)
Subject: Shared memory
Admins,
We have a GS140 6 cpu's and 20 GB of memory running oracle 8.1.7.4
with SGA set to 11 GB. When executing ipcs -b, shared memory adds up to 11
GB however when executing a vmstat -P it is showing about 2000000 free pages
( approx 16 GB free ). This does not seem consitant to me. Could anyone
point me in the right direction as to why my shared memory adds up to 11 GB
and I have 16 GB free. I will summarize.
TIA,
Chris Bryant
Unix Administrator
Dollar Thrifty Automotive Group
(918) 669-3213
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