[Novalug] Interesting memory usage on big server

Ken Kauffman kkauffman@headfog.com
Wed Sep 5 14:44:42 EDT 2007


Yeah. That's right.

Ken

-----Original Message-----
From: novalug-bounces@calypso.tux.org
[mailto:novalug-bounces@calypso.tux.org] On Behalf Of Ben Creitz
Sent: Wednesday, September 05, 2007 2:03 PM
To: novalug@calypso.tux.org
Subject: [Novalug] Interesting memory usage on big server

I am taking care of a big Dell server with 32 GB of RAM.  It runs
VMware Server, which in turns hosts two VMs.  Right now not much is
going on with the host or the VMs, they are idling.  The VMs are
allocated (in total) 1.5 GB of RAM.

The other day I noticed that out of the 32 GB of RAM on the physical
host, only about 15 GB were "free."  It happened to be a good time for
me to apply some Dell and RH updates and reboot... after the reboot I
watched with vmstat or 'free' as the available memory slowly trickled
away... for example this morning 'free' reported 28.9 GB available,
this afternoon only 27.34 GB.  top's results, sorted by memory, do not
show any processes using much... certainly not on the order of several
GBs.  So I opened a ticket with RH.

Here is the response I got from RH.  I wanted to share my observations
and RH's response with the group in case anybody out there has made
similar observations or has comments to add.  The memory activity
looks strange to me, but I suppose it may be attributable to something
in the way VMware server (or something else running on the system)
operates.

Red Hat's response:
"I have talked to a senior engineer to confirm this, and he said that
your situation is fine. The way that memory gets dealt with in Linux
is that when a program / data gets referenced, it gets put into
memory. That stays there even after the program is closed, so that the
next time the program is opened, it opens quickly. The data stays in
memory until memory is full, and then once that happens, memory starts
getting cleaned up."



Ben
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