[SGVLUG] used memory on a 4 GB system.

[Michael Proctor-Smith]

On 11/1/06, Jeff Carlson <jeff at ultimateevil.org> wrote:
> James Neff wrote:
> > I ran top and here are the results:
> >
> > top - 05:37:23 up 8 days,  1:44,  2 users,  load average: 0.00, 0.00, 0.00
> > Tasks:  99 total,   1 running,  98 sleeping,   0 stopped,   0 zombie
> > Cpu(s):  0.0% us,  0.1% sy,  0.0% ni, 99.9% id,  0.0% wa,  0.0% hi,
> > 0.0% si
> > Mem:   4039408k total,  4004660k used,    34748k free,    59444k buffers
> > Swap:  2031608k total,      128k used,  2031480k free,  3713780k cached
> >
> >  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> >    1 root      16   0  7196  704  592 S    0  0.0   0:00.99 init
> >    2 root      RT   0     0    0    0 S    0  0.0   0:00.11 migration/0
> >    3 root      34  19     0    0    0 S    0  0.0   0:00.00 ksoftirqd/0
> >    4 root      RT   0     0    0    0 S    0  0.0   0:00.00 watchdog/0
> >    5 root      RT   0     0    0    0 S    0  0.0   0:00.15 migration/1
> >    6 root      34  19     0    0    0 S    0  0.0   0:00.00 ksoftirqd/1
> >    7 root      RT   0     0    0    0 S    0  0.0   0:00.00 watchdog/1
> >    8 root      RT   0     0    0    0 S    0  0.0   0:00.03 migration/2
> >
> >
> > This is a dual Opteron system (2 processors) with 2 GB of RAM for each
> > processor.
>
> Just say you have 4GB of RAM.  Unless you've got a nice Sun or IBM with
> actual hardware partitioning, this idea of 2GB per processor is inaccurate.

Well that actually depends on how the motherboard is layed out as it
is an Opteron system which means the cpus have onboard memory
controllers so each processor could have its own memory. In an multi
cpu opteron based system you can end up with a very numa-like system.
But it is a fact that can be hidden from the OS as the processors
themselfs know how to access another cpus memory, but if your OS is
aware of that it is running on a Opteron system it can move memory
into memory belonging to the processor that the program is running on.
But again this is just what I remember from when AMD anounced the
Opteron. No one may be implemening there Motherboards that way, but
that would lead to the "secondary" cpus having degraded memory access
compared to the "primary" cpu(the one whos memory controller is
connected to the actual memory).

And as everyone else said having memory used is normal, and top is
only a good tool for finding out what is going wrong, and not for
analysis of memory usage. Basically you can find out which program has
gone nuts or if something has spawned a hundreds of zombie children.