linux-kernel - Re: [PATCH 4/8] proc: export more page flags in /proc/kpageflags

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Message-ID: <20090509075625.GA6843@localhost>
Date:	Sat, 9 May 2009 15:56:25 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Matt Mackall <mpm@...enic.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 4/8] proc: export more page flags in /proc/kpageflags

On Sat, May 09, 2009 at 01:59:14PM +0800, Ingo Molnar wrote:
> 
> * Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > > /proc/kpageflags should be done via the proper methods outlined 
> > > in the previous mails i wrote on this topic: for example by 
> > > using the 'object collections' abstraction i suggested. Clean 
> > > enumeration of all pages (files, tasks, etc.) and the definition 
> > > of histograms over it via free-form filter expressions is the 
> > > right way to do this. It would not only help other subsystems, 
> > > it would also be far more capable.
> > 
> > For the new interfaces(files etc.) I'd very like to use the ftrace 
> > interface. For the existing pagemap interfaces, if they can 
> > fulfill their targeted tasks, why bother making the shift?
> 
> Because they were a mistake to be merged? Because having them 
> fragments and thus weakens Linux instrumentation in general? 
> Because, somewhat hipocritically, other MM instrumentation patches 
> are being rejected under the pretense that they "do not matter" - 
> while instrumentation that provably _does_ matter (yours) is added 
> outside the existing instrumentation frameworks?
> 
> > When the pagemap interfaces cannot satisfy some new applications, 
> > and ftrace can provide a superset of the pagemap interfaces and 
> > shows clear advantages while meeting the new demands, then we can 
> > schedule tearing down of the old interface?
> 
> Yes. But meanwhile dont extend it ... otherwise this bad cycle will 
> never end. "Oh, we just added this to /proc/kpageflags too, why 
> should we go through the trouble of use the generic framework?"
> 
> Do you see my position?

Yes I can understand the merits of conforming to a generic framework.
But that alone is not enough. If you at the same time demonstrate some
clear technical advantages(flexibility, speed, simplicity etc.), then
it would be great.  (Let me work out some expectations for ftrace..)

Thanks,
Fengguang

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