linux-kernel - Re: Perf and ftrace [was Re: PyTimechart]

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Message-ID: <1273823631.5605.3614.camel@twins>
Date:	Fri, 14 May 2010 09:53:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pierre Tardy <tardyp@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org, arjan@...radead.org,
	ziga.mahkovec@...il.com, davem <davem@...emloft.net>
Subject: Re: Perf and ftrace [was Re: PyTimechart]

On Thu, 2010-05-13 at 12:31 -0400, Mathieu Desnoyers wrote:
> 
> In addition, this would play well with mmap() too: we can simply add a
> ring_buffer_get_mmap_offset() method to the backend (exported through another
> ioctl) that would let user-space know the start of the mmap'd buffer range
> currently owned by the reader. So we can inform user-space of the currently
> owned page range without even changing the underlying memory map. 

I still think keeping refs to splice pages is tricky at best. Suppose
they're spliced into the pagecache of a file, it could stay there for a
long time under some conditions.

Also, the splice-client (say the pagecache) and the mmap will both want
the pageframe to contain different information.
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