Re: Memory reporting on CentOS Linux

Linux strives to always use 100% of memory at any given time. Therefore the system will always throw free memory into swap cache. The kernel will (and can) take any memory away from the swap cache at any time for resident (physical) memory for processes.

That's why they have the column "-/+ buffers/cache:". That shows 46Gb Free RAM.

I cannot be the only person that has asked this question.

-----Original Message-----
From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Saturday, August 15, 2009 10:25 AM
To: Jeremy Carroll
Cc: Scott Carey; pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] Memory reporting on CentOS Linux

Jeremy Carroll <jeremy(dot)carroll(at)networkedinsights(dot)com> writes:
> I am thoroughly confused that TOP is reporting that I have 99% of my
> physical RAM free, while the process list suggests that some are
> taking ~8Gb of Resident (Physical) Memory. Any explanation as to why
> TOP is reporting this? I have a PostgreSQL 8.3 server with 48Gb of RAM
> on a Dell R610 server that is reporting that 46.5GB of RAM is free.

Exactly where do you draw that conclusion from? I see "free 138M".

It does look like there's something funny about top's accounting for
shared memory --- maybe it's counting it as "cached"? It's hardly
unusual for top to give bogus numbers in the presence of shared memory,
of course, but this seems odd :-(. With such large amounts of RAM
involved I wonder if there could be an overflow problem. You might file
a bug against top in whatever distro you are using.

regards, tom lane