linux-kernel - Re: [PATCH 3/9] readahead: record readahead patterns

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Date:	Wed, 30 Nov 2011 09:18:03 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, 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>
Subject: Re: [PATCH 3/9] readahead: record readahead patterns

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?

Something like this?

        $ cat /proc/self/fdinfo/2
        pos:    0
        flags:  0100002
+       ra_pattern:      initial
+       ra_size:         4

It may be some rapidly changing information, however in practical
should remain stable unless it's changing access pattern a lot.

> I could imagine a monitoring tool that you run on a process that
> tells you what pattern state the various file descriptors are in and how
> large the window is. That would be similar to the tools for
> monitoring network connections, which are extremly useful 
> in practice.

Yeah, the simplest form may be

        watch "head /proc/self/fdinfo/*"

Thanks,
Fengguang
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