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Message-ID: <525EF85A.6050302@intel.com>
Date: Wed, 16 Oct 2013 13:34:34 -0700
From: Dave Hansen <dave.hansen@intel.com>
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Subject: Re: [PATCH 2/2] mm: add a field to store names for private anonymous
 memory
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To: Colin Cross <ccross@android.com>, Minchan Kim <minchan@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>, Pekka Enberg <penberg@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Oleg Nesterov <oleg@redhat.com>, "Eric W. Biederman" <ebiederm@xmission.com>, Jan Glauber <jan.glauber@gmail.com>, John Stultz <john.stultz@linaro.org>, Rob Landley <rob@landley.net>, Andrew Morton <akpm@linux-foundation.org>, Cyrill Gorcunov <gorcunov@openvz.org>, Kees Cook <keescook@chromium.org>, "Serge E. Hallyn" <serge.hallyn@ubuntu.com>, David Rientjes <rientjes@google.com>, Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>, Michel Lespinasse <walken@google.com>, Tang Chen <tangchen@cn.fujitsu.com>, Robin Holt <holt@sgi.com>, Shaohua Li <shli@fusionio.com>, Sasha Levin <sasha.levin@oracle.com>, Johannes Weiner <hannes@cmpxchg.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, open@kvack.org, list@kvack.org, DOCUMENTATION <linux-doc@vger.kernel.org>open@kvack.orglist@kvack.org, MEMORY MANAGEMENT <linux-mm@kvack.org>

On 10/16/2013 01:00 PM, Colin Cross wrote:
>> > I guess this feature would be used with allocators tightly
>> > so my concern of kernel approach like this that it needs mmap_sem
>> > write-side lock to split/merge vmas which is really thing
>> > allocators(ex, tcmalloc, jemalloc) want to avoid for performance win
>> > that allocators have lots of complicated logic to avoid munmap which
>> > needs mmap_sem write-side lock but this feature would make it invalid.
> My expected use case is that the allocator will mmap a new large chunk
> of anonymous memory, and then immediately name it, resulting in taking
> the mmap_sem twice in a row. 

I guess the prctl (or a new one) _could_ just set a kernel-internal
variable (per-thread?) that says "point any future anonymous areas at
this name".  That way, you at least have the _possibility_ of not having
to do it for _every_ mmap().

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