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Subject: Re: Perf and ftrace [was Re: PyTimechart]
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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Date: Fri, 14 May 2010 09:53:51 +0200
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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.