linux-kernel - Re: [PATCH] proc: show readahead state in fdinfo

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Message-ID: <20111215094922.GA29981@elte.hu>
Date:	Thu, 15 Dec 2011 10:49:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] proc: show readahead state in fdinfo


* Wu Fengguang <fengguang.wu@...el.com> wrote:

> On Wed, Nov 30, 2011 at 01:57:43AM +0800, Andi Kleen wrote:
> > On Tue, Nov 29, 2011 at 09:09:03PM +0800, Wu Fengguang wrote:
> > > Record the readahead pattern in ra->pattern and extend the ra_submit()
> > > parameters, to be used by the next readahead tracing/stats patches.
> > 
> > I like this, could it be exported it a bit more formally in /proc for 
> > each file descriptor?
> 
> How about this?
> ---
> Subject: proc: show readahead state in fdinfo
> Date: Thu Dec 15 14:35:56 CST 2011
> 
> Append three readahead states to /proc/<PID>/fdinfo/<FD>:

Not a very good idea - please keep debug info under /debug as 
much as possible (as your original series did), instead of 
creating an ad-hoc insta-ABI in /proc.

In the long run we'd really like to retrieve such kind of 
information not even via ad-hoc exported info in /debug but via 
the standard event facilities: the tracepoints, if they are 
versatile enough, could be used to collect these stats and more.

Thanks,

	Ingo
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