linux-kernel - Re: [PATCH 4/5] perf record: mmap output file

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Date:	Tue, 19 Nov 2013 14:13:04 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org, jolsa@...hat.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 4/5] perf record: mmap output file - v5


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Nov 19, 2013 at 12:48:10PM +0100, Peter Zijlstra wrote:
> > And that does indeed seem to side-step the perf sw pagefault event, but
> > that is arguably a perf bug.
> 
> To clarify; mm/memory.c:handle_mm_fault() is where the VM counts its 
> generic PGFAULT event, but our perf sw event is in the arch fault 
> handler.
> 
> So they count different but related things.

I think that assymetry was intended: we didn't want to count 
'synchronous' pagefaults like get_user_pages() or mlock() bringing in 
pages, only asynchronous/real ones, or so.

Thanks,

	Ingo
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