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In-Reply-To: <20140506102925.GD11096@twins.programming.kicks-ass.net>
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	<20140506102925.GD11096@twins.programming.kicks-ass.net>
Date: Tue, 6 May 2014 07:57:02 -0700
Message-ID: <CA+55aFzt47Jpp-KK-ocLGgzYt_w-vheqFLfaGZOUSjwVrgGUtw@mail.gmail.com>
Subject: Re: [RFC] Heterogeneous memory management (mirror process address
 space on a device mmu).
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: j.glisse@gmail.com, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Mel Gorman <mgorman@suse.de>, "H. Peter Anvin" <hpa@zytor.com>, Andrew Morton <akpm@linux-foundation.org>, Linda Wang <lwang@redhat.com>, Kevin E Martin <kem@redhat.com>, Jerome Glisse <jglisse@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>, Johannes Weiner <jweiner@redhat.com>, Larry Woodman <lwoodman@redhat.com>, Rik van Riel <riel@redhat.com>, Dave Airlie <airlied@redhat.com>, Jeff Law <law@redhat.com>, Brendan Conoboy <blc@redhat.com>, Joe Donohue <jdonohue@redhat.com>, Duncan Poole <dpoole@nvidia.com>, Sherry Cheung <SCheung@nvidia.com>, Subhash Gutti <sgutti@nvidia.com>, John Hubbard <jhubbard@nvidia.com>, Mark Hairgrove <mhairgrove@nvidia.com>, Lucien Dunning <ldunning@nvidia.com>, Cameron Buschardt <cabuschardt@nvidia.com>, Arvind Gopalakrishnan <arvindg@nvidia.com>, Haggai Eran <haggaie@mellanox.com>, Or Gerlitz <ogerlitz@mellanox.com>, Sagi Grimberg <sagig@mellanox.com>, Shachar Raindel <raindel@mellanox.com>, Liran Liss <liranl@mellanox.com>, Roland Dreier <roland@purestorage.com>, "Sander, Ben" <ben.sander@amd.com>, "Stoner, Greg" <Greg.Stoner@amd.com>, "Bridgman, John" <John.Bridgman@amd.com>, "Mantor, Michael" <Michael.Mantor@amd.com>, "Blinzer, Paul" <Paul.Blinzer@amd.com>, "Morichetti, Laurent" <Laurent.Morichetti@amd.com>, "Deucher, Alexander" <Alexander.Deucher@amd.com>, "Gabbay, Oded" <Oded.Gabbay@amd.com>, Davidlohr Bueso <davidlohr@hp.com>

On Tue, May 6, 2014 at 3:29 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> So you forgot to CC Linus, Linus has expressed some dislike for
> preemptible mmu_notifiers in the recent past:

Indeed. I think we *really* should change that anonvma rwsem into an
rwlock. We had performance numbers that showed it needs to be done.

The *last* thing we want is to have random callbacks that can block in
this critical region. So now I think making it an rwlock is a good
idea just to make sure that never happens.

Seriously, the mmu_notifiers were misdesigned to begin with, and much
too deep. We're not screwing up the VM any more because of them.

                 Linus

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