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

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Message-ID: <20090428105603.GB25347@elte.hu>
Date:	Tue, 28 Apr 2009 12:56:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Fr馘駻ic 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>,
	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:

> Hi!
> 
> 2009/4/28 KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>:
> >> I guess the main question here is whether this approach will scale to
> >> something like kmalloc() or the page allocator in production
> >> environments. For any serious workload, the frequency of events is
> >> going to be pretty high.
> >
> > Immediate Values patch series makes zero-overhead to tracepoint
> > while it's not used.
> >
> > So, We have to implement to stop collect stastics way. it restore
> > zero overhead world.
> > We don't lose any performance by trace.
> 
> Sure but I meant the _enabled_ case here. kmalloc() (and the page 
> allocator to some extent) is very performance sensitive in many 
> workloads so you probably don't want to use tracepoints if you're 
> collecting some overall statistics (i.e. tracing all events) like 
> we do here.

That's where 'collect current state' kind of tracepoints would help 
- they could be used even without enabling any of the other 
tracepoints. And they'd still be in a coherent whole with the 
dynamic-events tracepoints.

So i'm not arguing against these techniques at all - and we can move 
on a wide scale from zero-overhead to lots-of-tracing-enabled models 
- what i'm arguing against is the splintering.

	Ingo
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