Swap and memory optimization
wmoran at potentialtech.com
Thu Oct 1 15:58:24 UTC 2009
In response to Dan Nelson <dnelson at allantgroup.com>:
> In the last episode (Oct 01), Bill Moran said:
> > bsd <bsd at todoo.biz> wrote:
> > > I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1
> > > Works quite well.
> > >
> > > As I plan to put 100 more mail accounts soon on the server I was
> > > wondering if the memory & swap was ok on the server considering these
> > > figures:
> > >
> > > last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38
> > > 125 processes: 1 running, 124 sleeping
> > > CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle
> > > Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free
> > > Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse
> > >
> > > Though It looks good to me - the server swaps a bit (between 8 to 14%)
> > > and there is not much memory left.
> > Looks like the server would run more smoothly with a bit more RAM. At
> > least an additional 256M, I would think, but considering the price of RAM,
> > you might as well just up it to 2G.
> The amount of used swap is much less important than whether you are actively
> swapping (if there are In/Out values on the Swap line in top, or if "vmstat
> 1" shows nonzero values in the pi/po columns). 160MB of used swap is fine
> if it's just unused daemons (getty, idle webserver, etc). More memory can
> never hurt, but it doesn't seem like it's urgently needed here.
I don't know about that, Dan. Especially considering it's a mail server
he's talking about, there's no RAM left for disk cache on that machine.
We've seen performance gains on our mail server by putting obscene
amounts of RAM into it. After a bit of use, FreeBSD ends up having 6.5G
of inactive RAM, which I assume is cache of mailboxes. The result is that
while watching gstat, the amount of disk reads is very low (since a lot
of data is already in RAM) and the IO is available to do fast writes when
new mail comes in.
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