Re: Linux mis-reporting memory

On 10/2/07, Decibel! <decibel@decibel.org> wrote:
> On Sep 21, 2007, at 4:43 AM, Gregory Stark wrote:
> > "Csaba Nagy" <nagy@ecircle-ag.com> writes:
> >
> >> On Fri, 2007-09-21 at 09:03 +0100, Gregory Stark wrote:
> >>>>> Mem:  32945280k total, 32871832k used,    73448k free,
> >>>>> 247432k buffers
> >>>>> Swap:  1951888k total,    42308k used,  1909580k free,
> >>>>> 30294300k cached
> >>>>
> >>> It seems to imply Linux is paging out sysV shared memory. In fact
> >>> some of
> >>> Heikki's tests here showed that Linux would do precisely that.
> >>
> >> But then why is it not reporting that in the "Swap: used"
> >> section ? It
> >> only reports 42308k used swap.
> >
> > Hm, good point.
> >
> > The other possibility is that Postgres just hasn't even touched a
> > large part
> > of its shared buffers.
>
> Sorry for the late reply...
>
> No, this is on a very active database server; the working set is
> almost certainly larger than memory (probably by a fair margin :( ),
> and all of the shared buffers should be in use.
>
> I'm leaning towards "top on linux == dumb".

Yeah, that pretty much describes it.  It's gotten better than it once
was.  But it still doesn't seem to be able to tell shared memory from
cache/buffer.