linux-kernel - Re: [PATCH v4 0/13] Uprobes v4

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Message-ID: <20100519060803.GB19957@linux.vnet.ibm.com>
Date:	Wed, 19 May 2010 11:38:03 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Steven Rostedt <rostedt@...dmis.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Roland McGrath <roland@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 0/13] Uprobes v4

> * Srikar Dronamraju (srikar@...ux.vnet.ibm.com) wrote:
> > Uprobes Patches
> > 
> > Changelog from v3:
> >   - Reverted to background page replacement as suggested by Peter Zijlstra.
> 
> Why ?
> 
> I'm not sure we reached any concensus about the need for a background page
> replacement.
> 
> Thanks,
> 
> Mathieu
> 

I was tested with access_process_vm(previous patchset) and the current
(background page replacement) and the results are the same. 

However Peter Zijlstra's contention still stands that we might be
relying on a undocumented feature in the hardware and the flipping the
pages isnt that hard or expensive.

Even Linus, (http://lkml.org/lkml/2010/1/27/87) had shown inclination
towards background page replacement. 

Also when uprobes implements global tracing support (i.e probing a
particular symbol in a dso across processes), it has to rely on
background page replacement. 

Hence I based this patchset on background page replacement rather than
on access_process_vm. Later On, if there is a consensus on using
access_process_vm, we can make the corresponding changes.

--
Thanks and Regards
Srikar
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