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

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Date:	Tue, 4 Dec 2007 14:25:37 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Dave Hansen <haveblue@...ibm.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mbligh@...gle.com
Subject: Re: [RFC PATCH] LTTng instrumentation mm (updated)

* Frank Ch. Eigler (fche@...hat.com) wrote:
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.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

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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