linux-kernel - Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags

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Date:	Tue, 28 Apr 2009 11:36:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Matt Mackall <mpm@...enic.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags


* Pekka Enberg <penberg@...helsinki.fi> wrote:

> > I have no idea how expensive tracepoints are but I suspect they 
> > don't make too much sense for this particular scenario. After 
> > all, kmemtrace is mainly interested in _allocation patterns_ 
> > whereas this patch seems to be more interested in "memory 
> > layout" type of things.
> 
> That said, I do foresee a need to be able to turn on more detailed 
> tracing after you've identified problematic areas from kpageflags 
> type of overview report. And for that, you almost certainly want 
> kmemtrace/tracepoints style solution with pid/function/whatever 
> regexp matching ftrace already provides.

yes. My point is that by having the latter, we pretty much have the 
former as well!

I 'integrate' traces all the time to get summary counts. This series 
of dynamic events:

  allocation
  page count up
  page count up
  page count down
  page count up
  page count up
  page count up
  page count up

integrates into: "page count is 6".

Note that "integration" can be done wholly in the kernel too, 
without going to the overhead of streaming all dynamic events to 
user-space, just to summarize data into counts, in-kernel. That is 
what the ftrace statistics framework and various ftrace plugins are 
about.

Also, it might make sense to extend the framework with a series of 
'get current object state' events when tracing is turned on. A 
special case of _that_ would in essence be what the /proc hack does 
now - just expressed in a much more generic, and a much more usable 
form.

	Ingo
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