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[40.107.13.80]) by mx.google.com with ESMTPS id hk20-v6si1220620ejb.104.2019.01.30.11.19.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 30 Jan 2019 11:19:55 -0800 (PST) Received-SPF: pass (google.com: domain of jgg@mellanox.com designates 40.107.13.80 as permitted sender) client-ip=40.107.13.80; Authentication-Results: mx.google.com; dkim=pass header.i=@Mellanox.com header.s=selector1 header.b=UzX6sHRR; spf=pass (google.com: domain of jgg@mellanox.com designates 40.107.13.80 as permitted sender) smtp.mailfrom=jgg@mellanox.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=mellanox.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Mellanox.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=1Gazb6Jp6B360Dq+MkPlp8a64vElOV9HlssPVSOq7PI=; b=UzX6sHRR56qy4HbKSErrFp0EcAChEVbY8N3BvrW9CePVEyW4vY+fpOg4QDe8VHDBBt5OBBuTZiGjJizPcNLUMnlotIiYO8iGAwlVBazrNyqdX9rYYOBJg4MOXFs06OsiWPWNeMApeoVn7ph52XRTWDS+ZxAgnsGIwSghnx4xzNA= Received: from DBBPR05MB6426.eurprd05.prod.outlook.com (20.179.42.80) by DBBPR05MB6395.eurprd05.prod.outlook.com (20.179.41.213) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1580.16; Wed, 30 Jan 2019 19:19:52 +0000 Received: from DBBPR05MB6426.eurprd05.prod.outlook.com ([fe80::24c2:321d:8b27:ae59]) by DBBPR05MB6426.eurprd05.prod.outlook.com ([fe80::24c2:321d:8b27:ae59%5]) with mapi id 15.20.1580.017; Wed, 30 Jan 2019 19:19:52 +0000 From: Jason Gunthorpe To: Logan Gunthorpe CC: Christoph Hellwig , Jerome Glisse , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Greg Kroah-Hartman , "Rafael J . Wysocki" , Bjorn Helgaas , Christian Koenig , Felix Kuehling , "linux-pci@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Marek Szyprowski , Robin Murphy , Joerg Roedel , "iommu@lists.linux-foundation.org" Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Thread-Topic: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Thread-Index: AQHUt/rA/dLikqWEmEaIytHIBNLPlqXGkyOAgAAJwICAAAX+AIAAEreAgAAFNYCAALluAIAAoq8AgAAIC4CAABKaAA== Date: Wed, 30 Jan 2019 19:19:52 +0000 Message-ID: <20190130191946.GD17080@mellanox.com> References: <20190129174728.6430-1-jglisse@redhat.com> <20190129174728.6430-4-jglisse@redhat.com> <20190129191120.GE3176@redhat.com> <20190129193250.GK10108@mellanox.com> <99c228c6-ef96-7594-cb43-78931966c75d@deltatee.com> <20190129205827.GM10108@mellanox.com> <20190130080208.GC29665@lst.de> <20190130174424.GA17080@mellanox.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: CO2PR04CA0185.namprd04.prod.outlook.com (2603:10b6:104:5::15) To DBBPR05MB6426.eurprd05.prod.outlook.com (2603:10a6:10:c9::16) authentication-results: spf=none (sender IP is ) smtp.mailfrom=jgg@mellanox.com; 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charset="us-ascii" Content-ID: <2608ADBADE66244CAF93015265B4523A@eurprd05.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: 141dbce2-fcb6-438c-3fab-08d686e7e8e6 X-MS-Exchange-CrossTenant-originalarrivaltime: 30 Jan 2019 19:19:52.2454 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR05MB6395 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jan 30, 2019 at 11:13:11AM -0700, Logan Gunthorpe wrote: >=20 >=20 > On 2019-01-30 10:44 a.m., Jason Gunthorpe wrote: > > I don't see why a special case with a VMA is really that different. >=20 > Well one *really* big difference is the VMA changes necessarily expose > specialized new functionality to userspace which has to be supported > forever and may be difficult to change.=20 The only user change here is that more things will succeed when creating RDMA MRs (and vice versa to GPU). I don't think this restricts the kernel implementation at all, unless we intend to remove P2P entirely.. Jason