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[140.211.169.12]) by mx.google.com with ESMTPS id g5si10200322pgk.402.2019.03.13.09.06.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Mar 2019 09:06:08 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 9909EE9C; Wed, 13 Mar 2019 16:06:07 +0000 (UTC) Date: Wed, 13 Mar 2019 09:06:04 -0700 From: Andrew Morton To: Jerome Glisse Cc: Dan Williams , Linux MM , Linux Kernel Mailing List , Ralph Campbell , John Hubbard , linux-fsdevel Subject: Re: [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem Message-Id: <20190313090604.968100351b19338cacbfa3bc@linux-foundation.org> In-Reply-To: <20190313001018.GA3312@redhat.com> References: <20190305141635.8134e310ba7187bc39532cd3@linux-foundation.org> <20190307094654.35391e0066396b204d133927@linux-foundation.org> <20190307185623.GD3835@redhat.com> <20190312152551.GA3233@redhat.com> <20190312190606.GA15675@redhat.com> <20190312145214.9c8f0381cf2ff2fc2904e2d8@linux-foundation.org> <20190313001018.GA3312@redhat.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 12 Mar 2019 20:10:19 -0400 Jerome Glisse wrote: > > You're correct. We chose to go this way because the HMM code is so > > large and all-over-the-place that developing it in a standalone tree > > seemed impractical - better to feed it into mainline piecewise. > > > > This decision very much assumed that HMM users would definitely be > > merged, and that it would happen soon. I was skeptical for a long time > > and was eventually persuaded by quite a few conversations with various > > architecture and driver maintainers indicating that these HMM users > > would be forthcoming. > > > > In retrospect, the arrival of HMM clients took quite a lot longer than > > was anticipated and I'm not sure that all of the anticipated usage > > sites will actually be using it. I wish I'd kept records of > > who-said-what, but I didn't and the info is now all rather dissipated. > > > > So the plan didn't really work out as hoped. Lesson learned, I would > > now very much prefer that new HMM feature work's changelogs include > > links to the driver patchsets which will be using those features and > > acks and review input from the developers of those driver patchsets. > > This is what i am doing now and this patchset falls into that. I did > post the ODP and nouveau bits to use the 2 new functions (dma map and > unmap). I expect to merge both ODP and nouveau bits for that during > the next merge window. > > Also with 5.1 everything that is upstream is use by nouveau at least. > They are posted patches to use HMM for AMD, Intel, Radeon, ODP, PPC. > Some are going through several revisions so i do not know exactly when > each will make it upstream but i keep working on all this. > > So the guideline we agree on: > - no new infrastructure without user > - device driver maintainer for which new infrastructure is done > must either sign off or review of explicitly say that they want > the feature I do not expect all driver maintainer will have > the bandwidth to do proper review of the mm part of the infra- > structure and it would not be fair to ask that from them. They > can still provide feedback on the API expose to the device > driver. The patchset in -mm ("HMM updates for 5.1") has review from Ralph Campbell @ nvidia. Are there any other maintainers who we should have feedback from? > - driver bits must be posted at the same time as the new infra- > structure even if they target the next release cycle to avoid > inter-tree dependency > - driver bits must be merge as soon as possible Are there links to driver patchsets which we can add to the changelogs? > Thing we do not agree on: > - If driver bits miss for any reason the +1 target directly > revert the new infra-structure. I think it should not be black > and white and the reasons why the driver bit missed the merge > window should be taken into account. If the feature is still > wanted and the driver bits missed the window for simple reasons > then it means that we push everything by 2 release ie the > revert is done in +1 then we reupload the infra-structure in > +2 and finaly repush the driver bit in +3 so we loose 1 cycle. > Hence why i would rather that the revert would only happen if > it is clear that the infrastructure is not ready or can not > be use in timely (over couple kernel release) fashion by any > drivers. I agree that this should be more a philosophy than a set of hard rules.