linux-kernel - Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)

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Message-ID: <20060922172859.GA11660@Krystal>
Date:	Fri, 22 Sep 2006 13:28:59 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)

* Ingo Molnar (mingo@...e.hu) wrote:
> > 
> > Yes, sorry, my mistake. This kind of fault is not as infrequent as you 
> > may think, as every newly allocated vmalloc region will cause vmalloc 
> > faults on every processes on the system that are trying to access 
> > them. I agree that it should not be a standard event people would be 
> > interested in.
> 
> most of the vmalloc area that is allocated on a typical system are 
> modules - and they get loaded on bootup and rarely unloaded. Even for 
> other vmalloc-ed areas like netfilter, the activation of them is during 
> bootup. So from that point on the number of vmalloc faults is quite low. 
> (zero on most systems) If you still want to trace it i'd suggest a 
> separate type of event for it.

Yes, with this typical vmalloc usage pattern in perspective, we completely
agree. We also agree on having a separate kind of event for this, as it requires
the tracer code to be vmalloc-fault-reentrant (very tricky).

Mathieu

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