Re: Better pagecache statistics ?

On Thu, 2005-12-01 at 16:15 -0200, Marcelo Tosatti wrote:
> > > I thought that it would be easy to use SystemTap for a such
> > > a purpose?
> > >
> > > The sys_read/sys_write example at
> > > http://www.redhat.com/magazine/011sep05/features/systemtap/ sounds
> > > interesting.
> > >
> > > What I'm I missing?
> >
> > Well, Few things:
> >
> > 1) We have to have those probes present in the system all the time
> > collecting the information when read/write happens, maintaining it
> > and spitting it out. Since its kernel probe, all this data will be
> > in the kernel.
>
> Yeah, there is some overhead.
>
> > 2) If we want to do this accounting (and you don't have those probes
> > installed already) - we can't capture what happened earlier.
>
> I suppose that the vast majority of situations where such information is
> needed are special anyway?
>
> Why do you need it around all the time?

Otherwise, we need to insert hooks and ask the customer to reproduce
the problem :(

> > 3) probing sys_read/sys_write() are going to tell you how much
> > a data a process did read or wrote - but its not going to tell you
> > how much is in the cache (now or 10 minutes later).
>
> Sure, that was just an example - need to insert probes
> on the correct places.


Okay, I miss understood.


Thanks,
Badari

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: Better pagecache statistics ?
    ... >> a purpose? ... > collecting the information when read/write happens, ... Since its kernel probe, ... > 2) If we want to do this accounting (and you don't have those probes ...
    (Linux-Kernel)
  • Re: Pioneer anomaly
    ... still ongoing. ... Last I heard, "we" have been wanting to send up other probes, for the ... purpose of looking again for the effect. ...
    (sci.physics.relativity)
  • FS Data acquisition probes for Fluke 9010A from $89
    ... I just picked up a mess of probes. ... One has a missing side of the case but ... Prev by Date: ...
    (rec.games.video.arcade.collecting)
  • Re: Point Inside a triangle
    ... inside a triangle, or where can I find one that is relatively simple to understand. ... purpose than just that (: Efficient Point Probes). ... But do _you_ know in what context the original poster is going to use the technique? ...
    (sci.math)