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Date: Fri, 12 Jul 2013 11:00:46 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/2] mm: add a field to store names for private anonymous
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To: Ingo Molnar <mingo@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>, Colin Cross <ccross@android.com>, linux-kernel@vger.kernel.org, Kyungmin Park <kmpark@infradead.org>, Christoph Hellwig <hch@infradead.org>, John Stultz <john.stultz@linaro.org>, "Eric W. Biederman" <ebiederm@xmission.com>, Dave Hansen <dave.hansen@intel.com>, Rob Landley <rob@landley.net>, Andrew Morton <akpm@linux-foundation.org>, Cyrill Gorcunov <gorcunov@openvz.org>, David Rientjes <rientjes@google.com>, Davidlohr Bueso <dave@gnu.org>, Kees Cook <keescook@chromium.org>, Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>, Michel Lespinasse <walken@google.com>, Rik van Riel <riel@redhat.com>, Konstantin Khlebnikov <khlebnikov@openvz.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, David Howells <dhowells@redhat.com>, Arnd Bergmann <arnd@arndb.de>, Dave Jones <davej@redhat.com>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, Oleg Nesterov <oleg@redhat.com>, Shaohua Li <shli@fusionio.com>, Sasha Levin <sasha.levin@oracle.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Johannes Weiner <hannes@cmpxchg.org>, linux-doc@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>

On Fri, Jul 12, 2013 at 10:44:06AM +0200, Ingo Molnar wrote:
> It makes tons of sense.
> 
> Just like we have a task's cmd-name it makes a lot of sense to name 
> objects in a human readable fashion, to help debugging, instrumentation, 
> performance analysis, etc.
> 
> Yes, in theory user-space could do all that. That's not the point: the 
> point is to make it fast, easy enough and to have a central version (the 
> kernel).
> 
> Doing it via temporary files has various disadvantages:

We need those files anyway.. The current proposal is that the entire VMA has a
single userspace pointer in it. Or rather a 64bit value.

> I guess the real question is not whether it's useful, I think it clearly 
> is. The question should be: are there real downsides? Does the addition to 
> the anon mmap field blow up the size of vma_struct by a pointer, or is 
> there still space?

I don't see how the single u64 is useful at all for perf; you can have at most
one u64 per page; that's not nearly enough to put symbol information in.
Therefore we still require external files.

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