linux-kernel - Re: [patch] tracing/mm: add page frame snapshot trace

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Date:	Sat, 9 May 2009 17:43:16 +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] tracing/mm: add page frame snapshot trace

On Sat, May 09, 2009 at 05:24:31PM +0800, Ingo Molnar wrote:
> 
> * Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > Hi Ingo,
> > 
> > On Sat, May 09, 2009 at 02:27:58PM +0800, Ingo Molnar wrote:
> > > 
> > > * Wu Fengguang <fengguang.wu@...el.com> wrote:
> > > 
> > > > > So this should be done in cooperation with instrumentation 
> > > > > folks, while improving _all_ of Linux instrumentation in 
> > > > > general. Or, if you dont have the time/interest to work with us 
> > > > > on that, it should not be done at all. Not having the 
> > > > > resources/interest to do something properly is not a license to 
> > > > > introduce further instrumentation crap into Linux.
> > > > 
> > > > I'd be glad to work with you on the 'object collections' ftrace 
> > > > interfaces.  Maybe next month. For now my time have been allocated 
> > > > for the hwpoison work, sorry!
> > > 
> > > No problem - our offer still stands: we are glad to help out with 
> > > the instrumentation side bits. We'll even write all the patches for 
> > > you, just please help us out with making it maximally useful to 
> > > _you_ :-)
> > 
> > Thank you very much!
> > 
> > The good fact is, 2/3 of the code and experiences can be reused.
> > 
> > > Find below a first prototype patch written by Steve yesterday and 
> > > tidied up a bit by me today. It can also be tried on latest -tip:
> > > 
> > >   http://people.redhat.com/mingo/tip.git/README
> > > 
> > > This patch adds the first version of the 'object collections' 
> > > instrumentation facility under /debug/tracing/objects/mm/. It has a 
> > > single control so far, a 'number of pages to dump' trigger file:
> > > 
> > > To dump 1000 pages to the trace buffers, do:
> > > 
> > >   echo 1000 > /debug/tracing/objects/mm/pages/trigger
> > > 
> > > To dump all pages to the trace buffers, do:
> > > 
> > >   echo -1 > /debug/tracing/objects/mm/pages/trigger
> > 
> > That is not too intuitive, I'm afraid.
> 
> This was just a first-level approximation - and it matches the usual 
> "0xffffffff means infinite" idiom.

8^)

> How about changing it from 'trigger' to 'dump_range':

That's a better name!

>    echo "*" > /debug/tracing/objects/mm/pages/dump_range
> 
> being a shortcut for 'dump all'?

No I'm not complaining about -1. That's even better than "*",
because the latter can easily be expanded by shell ;)

> And:
> 
>    echo "1000 2000" > /debug/tracing/objects/mm/pages/dump_range
> 
> ?

Now it's much more intuitive!

> The '1000' is the offset where the dumping starts, and 2000 is the 
> size of the dump.

Ah the second parameter 2000 can easily be taken as "end"..

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