linux-kernel - Re: [PATCH] Add tracepoints to track pagecache transition

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Message-Id: <20090218091726.898D.A69D9226@jp.fujitsu.com>
Date:	Wed, 18 Feb 2009 09:29:04 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Atsushi Tsuji <a-tsuji@...jp.nec.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Jason Baron <jbaron@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Kazuto Miyoshi <miyoshi@...ux.bs1.fc.nec.co.jp>,
	rostedt@...dmis.org, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH] Add tracepoints to track pagecache transition

Hi Frederic,

> > And, both function is freqentlly called one.
> > I worry about performance issue. can you prove no degression?
> 
> It would be very hard to prove. Tracepoints are very cheap in that they only
> add the overhead of a single branch check while off.

this is typical reviewing comment.

Memory folks adage says,
	Don't believe theory, you believe benchmark result.

I don't oppose your theorical background opinion :)


> But are there some plans about writing a tracer or so for pagecache?



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