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Message-ID: <20090428091508.GA21085@elte.hu>
Date: Tue, 28 Apr 2009 11:15:08 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Pekka Enberg <penberg@...helsinki.fi>
Cc: Andi Kleen <andi@...stfloor.org>,
Wu Fengguang <fengguang.wu@...el.com>,
Steven Rostedt <rostedt@...dmis.org>,
Frédéric Weisbecker <fweisbec@...il.com>,
Larry Woodman <lwoodman@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Matt Mackall <mpm@...enic.com>,
Alexey Dobriyan <adobriyan@...il.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags
* Pekka Enberg <penberg@...helsinki.fi> wrote:
> Hi Andi,
>
> On Tue, 2009-04-28 at 09:40 +0200, Andi Kleen wrote:
> > > I think i have to NAK this kind of ad-hoc instrumentation of kernel
> > > internals and statistics until we clear up why such instrumentation
> >
> > I think because it has zero fast path overhead and can be used
> > any time without enabling anything special.
( That's a dubious claim in any case - tracepoints are very cheap.
And they could be made even cheaper and such efforts would benefit
all the tracepoint users so it's a prime focus of interest.
Andi is a SystemTap proponent, right? I saw him oppose pretty much
everything built-in kernel tracing related. I consider that a
pretty extreme position. )
> Yes, zero overhead is important for certain things (like
> CONFIG_SLUB_STATS, for example). However, putting slab allocator
> specific checks in fs/proc looks pretty fragile to me. It would be
> nice to have this under the "kmemtrace umbrella" so that there's
> just one place that needs to be fixed up when allocators change.
>
> Also, while you probably don't want to use tracepoints for this
> kind of instrumentation, you might want to look into reusing the
> ftrace reporting bits.
Exactly - we have a tracing and statistics framework for a reason.
Ingo
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