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

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Date:	Tue, 8 Oct 2013 11:42:06 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions

On Tue, Oct 8, 2013 at 11:36 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Oct 08, 2013 at 09:15:30AM +0200, Stephane Eranian wrote:
>> Yes, it is but I am trying to see whether or not we could unify that and
>> use a single u64 number to uniquely identify each mapping.
>
> No you cannot; two unrelated executables which have distinct mm_ids can
> easily mmap() the same shared file.

That seems to indicate the mm_ids is not attached to the right level of VM
data structure. But I am okay with keeping it that way and stashing the mm_id
as a pseudo inode number for the case of non file-backed mappings. If we
say maj=min=ino=gen=0 means no "info", then any other combinations can
be used to identify identical mappings. We use actual min,maj, ino, gen
for file backed, and maj=min=gen=0 + ino = mm_ids for the other cases.
That should work, shouldn't it?
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