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[213.95.11.211]) by mx.google.com with ESMTPS id u185si796379wmg.131.2019.01.29.23.52.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 29 Jan 2019 23:52:57 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) client-ip=213.95.11.211; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by newverein.lst.de (Postfix, from userid 2407) id C07BF68CEC; Wed, 30 Jan 2019 08:52:56 +0100 (CET) Date: Wed, 30 Jan 2019 08:52:56 +0100 From: Christoph Hellwig To: Logan Gunthorpe Cc: Jerome Glisse , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Rafael J . Wysocki" , Bjorn Helgaas , Christian Koenig , Felix Kuehling , Jason Gunthorpe , linux-pci@vger.kernel.org, dri-devel@lists.freedesktop.org, Christoph Hellwig , 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 Message-ID: <20190130075256.GA29665@lst.de> References: <20190129174728.6430-1-jglisse@redhat.com> <20190129174728.6430-4-jglisse@redhat.com> <20190129191120.GE3176@redhat.com> <20190129194418.GG3176@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) 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 Tue, Jan 29, 2019 at 01:43:02PM -0700, Logan Gunthorpe wrote: > It's hard to reason about an interface when you can't see what all the > layers want to do with it. Most maintainers (I'd hope) would certainly > never merge code that has no callers, and for much the same reason, I'd > rather not review patches that don't have real use case examples. Yes, we should never review, nevermind merge code without users. We had one example recently where this was not followed, which was HMM and that turned out to be a desaster.