[CentOS] Swap memory: I can't reconcile this stuff.

Tue Jun 6 00:50:31 UTC 2006
William L. Maltby <BillsCentOS at triad.rr.com>

On Mon, 2006-06-05 at 20:02 -0300, Rodrigo Barbosa wrote:
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> On Mon, Jun 05, 2006 at 06:45:10PM -0400, William L. Maltby wrote:
> ><snip>

> > 
> > Mem:    775708k total,   764752k used,    10956k free,    60780k buffers
> > Swap:  1572856k total,      160k used,  1572696k free,   377324k cached
> > 
> >   PID  VIRT  RES  SHR %MEM SWAP COMMAND
> > 24729  127m  32m  15m  4.3  94m evolution
> >  3409 97220 5268 4304  0.7  89m evolution-data-
> >  2851  115m  36m 7120  4.8  79m X
> >  3359 19904 6128 5316  0.8  13m gnome-volume-ma
> (...)
> >  3355 14768 7524 5984  1.0 7244 metacity
> >  7182 10328 3436 2280  0.4 6892 sendmail
> > 18501 11080 4248 1912  0.5 6832 cupsd
> > 
> > Note that the summary line says 160k of swap is used. The man pages say
> > the summary and the details under "SWAP" are both reported in "k". No
> > mention of "m" is made, I presume that it means "megabytes"?
> > <snip>

> > Now, if I treat all those numbers ending in "m" as megabytes, it doesn't
> > take long to see that I've been lied to somewhere along the way. Or
> > alternatively, I'm dense and "Just Don't Get It" (TM).
> > 
> > Any help?
> 
> I can see two possible explanations for this. Maybe both in conjunction.
> 
> One is that you get getting multiple entries for the same processes,
> but different threads. That used to be the way of it up until .. humm,
> not sure ... 2.4, I guess. Not sure exactly how it works these days. I would
> have to check.
> 
> The other is the overcommit kernel feature. It is possible the kernel
> is overcommiting memory, and thus showing more than it really in
> use.
> 
> One last thing possible (just thought about it) is that top is adding
> more than one namespace to those totals. Maybe shared memory (/dev/shm ?).
> Or any other possible namespace.
> 
> I agree it does seem odd, and I have seen this kind of stuff happening
> before. Once I started hunting it down, and found the reason for it.
> It was some time ago (2.2 ? 2.4 ? Not sure), so I'm reasonably sure
> it is not the same reason these days. But I hope I gave you are
> least some pointers for where to start looking.

Would I be correct if I summarized as "Looks like a bug, and possibly a
regression that you had seen before"? I think then I'll first start by
seeing if there is an open bug somewhere. I hate having to chase code
right now as I'm trying to improve my knowledge and use of sendmail,
DNS, ... and a whole host of other things that flew by me over the
years. <*sigh*>

Anyhow, thanks for getting back to me. I'm going to try to work
investigation of this in with the other things I've got going.

> - -- 
> Rodrigo Barbosa <rodrigob at suespammers.org>
> <snip sig stuff>

-- 
Bill
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