Re: [PATCH 2/2] mm: add a field to store names for private anonymous memory

From: Pekka Enberg <penberg@kernel.org>
To: Colin Cross <ccross@android.com>
Cc: 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>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"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>,
	Ingo Molnar <mingo@kernel.org>,
	linux-doc@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/2] mm: add a field to store names for private anonymous memory
Date: Fri, 12 Jul 2013 08:39:14 +0300	[thread overview]
Message-ID: <51DF9682.9040301@kernel.org> (raw)
In-Reply-To: <1373596462-27115-2-git-send-email-ccross@android.com>

On 07/12/2013 05:34 AM, Colin Cross wrote:
> Userspace processes often have multiple allocators that each do
> anonymous mmaps to get memory.  When examining memory usage of
> individual processes or systems as a whole, it is useful to be
> able to break down the various heaps that were allocated by
> each layer and examine their size, RSS, and physical memory
> usage.
>
> This patch adds a user pointer to the shared union in
> vm_area_struct that points to a null terminated string inside
> the user process containing a name for the vma.  vmas that
> point to the same address will be merged, but vmas that
> point to equivalent strings at different addresses will
> not be merged.
>
> Userspace can set the name for a region of memory by calling
> prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
> Setting the name to NULL clears it.
>
> The names of named anonymous vmas are shown in /proc/pid/maps
> as [anon:<name>] and in /proc/pid/smaps in a new "Name" field
> that is only present for named vmas.  If the userspace pointer
> is no longer valid all or part of the name will be replaced
> with "<fault>".
>
> The idea to store a userspace pointer to reduce the complexity
> within mm (at the expense of the complexity of reading
> /proc/pid/mem) came from Dave Hansen.  This results in no
> runtime overhead in the mm subsystem other than comparing
> the anon_name pointers when considering vma merging.  The pointer
> is stored in a union with fieds that are only used on file-backed
> mappings, so it does not increase memory usage.
>
> Signed-off-by: Colin Cross <ccross@android.com>

Ingo, PeterZ, is this something worthwhile for replacing our
current JIT symbol hack with perf?

			Pekka

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