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[209.132.183.28]) by mx.google.com with ESMTPS id z54si1526880qth.393.2019.03.12.18.01.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 18:01:00 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0A9133082E71; Wed, 13 Mar 2019 01:01:00 +0000 (UTC) Received: from redhat.com (ovpn-116-53.phx2.redhat.com [10.3.116.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2447217184; Wed, 13 Mar 2019 01:00:59 +0000 (UTC) Date: Tue, 12 Mar 2019 21:00:57 -0400 From: Jerome Glisse To: Dan Williams Cc: Andrew Morton , 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: <20190313010056.GA3402@redhat.com> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Wed, 13 Mar 2019 01:01:00 +0000 (UTC) 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, Mar 12, 2019 at 05:46:51PM -0700, Dan Williams wrote: > On Tue, Mar 12, 2019 at 5:10 PM Jerome Glisse wrote: > > > > On Tue, Mar 12, 2019 at 02:52:14PM -0700, Andrew Morton wrote: > > > On Tue, 12 Mar 2019 12:30:52 -0700 Dan Williams wrote: > > > > > > > On Tue, Mar 12, 2019 at 12:06 PM Jerome Glisse wrote: > > > > > On Tue, Mar 12, 2019 at 09:06:12AM -0700, Dan Williams wrote: > > > > > > On Tue, Mar 12, 2019 at 8:26 AM Jerome Glisse wrote: > > > > [..] > > > > > > > Spirit of the rule is better than blind application of rule. > > > > > > > > > > > > Again, I fail to see why HMM is suddenly unable to make forward > > > > > > progress when the infrastructure that came before it was merged with > > > > > > consumers in the same development cycle. > > > > > > > > > > > > A gate to upstream merge is about the only lever a reviewer has to > > > > > > push for change, and these requests to uncouple the consumer only > > > > > > serve to weaken that review tool in my mind. > > > > > > > > > > Well let just agree to disagree and leave it at that and stop > > > > > wasting each other time > > > > > > > > I'm fine to continue this discussion if you are. Please be specific > > > > about where we disagree and what aspect of the proposed rules about > > > > merge staging are either acceptable, painful-but-doable, or > > > > show-stoppers. Do you agree that HMM is doing something novel with > > > > merge staging, am I off base there? > > > > > > 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. > > - 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 > > What about EXPORT_SYMBOL_GPL? I explained why i do not see value in changing export, but i will not oppose that change either. > > 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. > > I think that pain is reasonable. > > > 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. > > This seems too generous to me, but in the interest of moving this > discussion forward let's cross that bridge if/when it happens. > Hopefully the threat of this debate recurring means consumers put in > the due diligence to get things merged at infrastructure + 1 time.