From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-qa0-f44.google.com (mail-qa0-f44.google.com [209.85.216.44])
	by kanga.kvack.org (Postfix) with ESMTP id 3CCDC8299E
	for <linux-mm@kvack.org>; Tue,  6 May 2014 11:00:28 -0400 (EDT)
Received: by mail-qa0-f44.google.com with SMTP id j7so3069517qaq.3
        for <linux-mm@kvack.org>; Tue, 06 May 2014 08:00:27 -0700 (PDT)
Received: from mail-qg0-x230.google.com (mail-qg0-x230.google.com [2607:f8b0:400d:c04::230])
        by mx.google.com with ESMTPS id t40si4511125qge.104.2014.05.06.08.00.26
        for <linux-mm@kvack.org>
        (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128);
        Tue, 06 May 2014 08:00:27 -0700 (PDT)
Received: by mail-qg0-f48.google.com with SMTP id i50so8004285qgf.21
        for <linux-mm@kvack.org>; Tue, 06 May 2014 08:00:26 -0700 (PDT)
Date: Tue, 6 May 2014 11:00:17 -0400
From: Jerome Glisse <j.glisse@gmail.com>
Subject: Re: [RFC] Heterogeneous memory management (mirror process address
 space on a device mmu).
Message-ID: <20140506150014.GA6731@gmail.com>
References: <1399038730-25641-1-git-send-email-j.glisse@gmail.com>
 <20140506102925.GD11096@twins.programming.kicks-ass.net>
 <CA+55aFzt47Jpp-KK-ocLGgzYt_w-vheqFLfaGZOUSjwVrgGUtw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CA+55aFzt47Jpp-KK-ocLGgzYt_w-vheqFLfaGZOUSjwVrgGUtw@mail.gmail.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>, 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 06, 2014 at 07:57:02AM -0700, Linus Torvalds wrote:
> 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

So question becomes how to implement process address space mirroring
without pinning memory and track cpu page table update knowing that
device page table update is unbound can not be atomic from cpu point
of view.

Cheers,
Jerome

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>