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

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Message-ID: <20100519173806.GA3319@linux.vnet.ibm.com>
Date:	Wed, 19 May 2010 23:08:06 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	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

* Peter Zijlstra <peterz@...radead.org> [2010-05-19 16:17:40]:

> On Wed, 2010-05-19 at 11:38 +0530, Srikar Dronamraju wrote:
> > 
> > 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. 
> 
> Uhm, how so?

For global tracing we cant use access_process_vm. The equivalent to
access_process_vm for global tracing would be to use copy_to_user.

However I am sure people wouldnt be happy using copy_to_user on a page
that other processes could have mapped. 

So that leaves us with background page replacement method. 
I do agree that we will not be using the same routine. But the technique
should be something similar(or do you disagree?). 

Or do you suggest any alternative methods for global tracing?

--
Thanks and Regards
Srikar
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