Re: [RFC PATCH] LTTng instrumentation mm (updated)

Mathieu Desnoyers
2007-12-04T19:30:46Z

* Frank Ch. Eigler (fche@redhat.com) wrote:
> Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> writes:
>
> > [...]
> >> > We would like to be able to tell which swap file the information has
> >> > been written to/read from at any given time during the trace.
> >>
> >> Oh, tracing is expected to be on at all times? I figured someone would
> >> encounter a problem, then turn it on to dig down a little deeper, then
> >> turn it off.
> >
> > Yep, it can be expected to be on at all times, especially on production
> > systems using "flight recorder" tracing to record information in a
> > circular buffer [...]
>
> Considering how early in the boot sequence swap partitions are
> activated, it seems optimistic to assume that the monitoring equipment
> will always start up in time to catch the initial swapons. It would
> be more useful if a marker parameter was included in the swap events
> to let a tool/user map to /proc/swaps or a file name.
>
> - FChE

Not early at all ? We have userspace processes running.. this is _late_
in the boot sequence! ;)

Anyhow, that I have now is a combination including your proposal :

- I dump the swapon/swapoff events.
- I also dump the equivalent of /proc/swaps (with kernel internal
information) at trace start to know what swap files are currently
used.

Does it sound fair ?

Mathieu