linux-kernel - Re: [RFC] perf: mmap2 not covering VM

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Date:	Wed, 9 Oct 2013 11:54:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions


* David Ahern <dsahern@...il.com> wrote:

> On 10/8/13 1:54 PM, Stephane Eranian wrote:
> >>>If the current MMAP2 is not a complete solution for what you (Google)
> >>>need, should support be reverted before 3.12 is released? No sense in
> >>>making this part of the forever API if more work is needed on it.
> >>
> >>Instead of a full revert we could just turn off the ABI portion minimally
> >>and not recognize it for now. Assuming a more complete solution is in the
> >>works for v3.13.
> >>
> >That's a possibility. They are also pieces in the perf tool itself.
> >We could certainly make the attr->mmap2 bit disappear.
> >
> >I think it boils down to how can we uniquely identify virtual
> >mapping to the same physical data either via shmat(), files, VM_CLONE.
> >We had all covered but the last case with the ino approach. We don't have
> >a solution for VM_CLONE yet.
> >
> 
> I was mainly thinking the 2 parts that generate MMAP2 events: kernel 
> side it's the mmap2 attribute and perf_event_mmap_output; userspace side 
> it's perf_event__synthesize_mmap_event. Certainly the rest of the 
> plumbing can be left in place until the solution is refined as needed.

Could some of you please send a patch ASAP?

Thanks,

	Ingo
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