From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 307B2C43381 for ; Wed, 13 Mar 2019 00:47:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA01D214AE for ; Wed, 13 Mar 2019 00:47:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="15ssqlbM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726490AbfCMArE (ORCPT ); Tue, 12 Mar 2019 20:47:04 -0400 Received: from mail-ot1-f68.google.com ([209.85.210.68]:38060 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726365AbfCMArE (ORCPT ); Tue, 12 Mar 2019 20:47:04 -0400 Received: by mail-ot1-f68.google.com with SMTP id m1so231161otf.5 for ; Tue, 12 Mar 2019 17:47:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mLj4qcCQx2Pn+uXcFJ85DvqflvBkrhEGWb75t5OlUng=; b=15ssqlbMFEuple84d+nWcgJNQ+bAE69hLg9vgjJlg8ROS8W3lxVvATNXiK5GYlrhH5 vM7DtUN6LU4Nph550Md5x6+LDDByKkR7x0CEvquaxELcbFthbflmxYnASUgkD0EcakZe 6EfSI0yb+3TdgO3bdr1FKqY8Bv9kp6XCmarSWTU7v334wVAU2RIov9oG+wuBqtG/AjQc MYVlQ90xUZw2zcLNTx2lciilggH14qDDAJRCKbtzx81ayHUI/yb4vlytEJkPVEnXT7R/ r3hhcDUTZgb/5c4rc2pQF7eiUv+g7JgXXvk8qoLAKpTXRyphRw+B1TRkAJSsoGQy/GMA 1nFQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mLj4qcCQx2Pn+uXcFJ85DvqflvBkrhEGWb75t5OlUng=; b=uiZSuTRGu9PFhx2KUgHBcQVzF6tHGiprG528LR83Gf3WwvJ8OVoWTbHU4Fixy3AeBe CIhvGChOu7xUE9mw1gy3U6wB2ehIv0A+wKP7xPnCkF/IenlVL8xJF1x4pGRypLM6uxf7 Qw85HLGU8H5My9Wlap1YvjZsjnJsrcfeP+zr2cTjDy+pUuZjW9xbvx2QX8GC7dDHAfbi FsWcJpriGcU5aBLfHNhsKNoUJqwLNdH0srGF+HSU/N7wczh4WEtFD2Tm+lzOl7ovhbBk 3Lvqgb7nJu45gcSXGmv38hy3blMBg3T9R13h7MgI3Ux/QgMqCKPBQ5Tq+I1S1wOf41to fMOw== X-Gm-Message-State: APjAAAUPeRd7867sScg5TSrm4vdNjaaToav9lgCBaxMZ+OjPwEvSfXqQ IFEv8r499t8X9+l+OjEuaQY8mrklcZ+dUhw6LbZaNA== X-Google-Smtp-Source: APXvYqw0Mpk2Nx7zxk3e2cteUAAoUeiLm5q90A8CIm9oOmu4nbmapF5pCiWJ9T7GcsgSrbuN3twHgSfOBxhzOCdFnjc= X-Received: by 2002:a9d:760a:: with SMTP id k10mr1705011otl.367.1552438022857; Tue, 12 Mar 2019 17:47:02 -0700 (PDT) MIME-Version: 1.0 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> In-Reply-To: <20190313001018.GA3312@redhat.com> From: Dan Williams Date: Tue, 12 Mar 2019 17:46:51 -0700 Message-ID: Subject: Re: [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem To: Jerome Glisse Cc: Andrew Morton , Linux MM , Linux Kernel Mailing List , Ralph Campbell , John Hubbard , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > 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.