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

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Message-ID: <20090428092918.GC21085@elte.hu>
Date:	Tue, 28 Apr 2009 11:29:18 +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.

My point is that the allocation patterns can be derived from dynamic 
events. We can build a map of everything if we know all the events 
that led up to it. Doing:

  echo 3 > /proc/sys/vm/drop_caches

will clear 99% of the memory allocations, so we can build a new map 
from scratch just about anytime. (and if boot allocations are 
interesting they can be traced too)

_And_ via this angle we'll also have access to the dynamic events, 
in a different 'view' of the same tracepoints - which is obviously 
very useful for different purposes.

	Ingo
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