From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 1A570607C7
Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=lst.de
Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752319AbeFFHHF (ORCPT <rfc822;monsieuricon@codeaurora.org>
        + 25 others); Wed, 6 Jun 2018 03:07:05 -0400
Received: from verein.lst.de ([213.95.11.211]:36081 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751899AbeFFHHE (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 6 Jun 2018 03:07:04 -0400
Date: Wed, 6 Jun 2018 09:14:18 +0200
From: Christoph Hellwig <hch@lst.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>,
        Dave Airlie <airlied@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        Christoph Hellwig <hch@lst.de>, Michal Hocko <mhocko@suse.com>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/5] mm: rework hmm to use devm_memremap_pages
Message-ID: <20180606071418.GA7660@lst.de>
References: <CAPcyv4hVERZoqWrCxwOkmM075OP_ada7FiYsQgokijuWyC1MbA@mail.gmail.com> <CAPM=9tzMJq=KC+ijoj-JGmc1R3wbshdwtfR3Zpmyaw3jYJ9+gw@mail.gmail.com> <CAPcyv4g2XQtuYGPu8HMbPj6wXqGwxiL5jDRznf5fmW4WgC2DTw@mail.gmail.com> <CAPM=9twm=17t=2=M27ELB=vZWzpqM7GuwCUsC891jJ0t3JM4vg@mail.gmail.com> <CAPcyv4jTty4k1xXCOWbeRjzv-KjxNH1L4oOkWW1EbJt66jF4_w@mail.gmail.com> <20180605184811.GC4423@redhat.com> <CAPM=9twgL_tzkPO=V2mmecSzLjKJkEsJ8A4426fO2Nuus0N_UQ@mail.gmail.com> <CAPcyv4gSEYdnJKd=D-_yc3M=sY0HWjYzYhh5ha-v7KA4-40dsg@mail.gmail.com> <20180606000822.GE4423@redhat.com> <CAPcyv4gsS4xDXahZdOggURBHS2y-oJ5tPG9vXPDdY2p6jPufxA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAPcyv4gsS4xDXahZdOggURBHS2y-oJ5tPG9vXPDdY2p6jPufxA@mail.gmail.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jun 05, 2018 at 06:33:04PM -0700, Dan Williams wrote:
> Unless the nouveau patches are using the entirety of what is already
> upstream for HMM, we should look to pare HMM back.
> 
> There is plenty of precedent of building a large capability
> out-of-tree and piecemeal merging it later, so I do not buy the
> "chicken-egg" argument. The change in the export is to make sure we
> don't repeat this backward "merge first, ask questions later" mistake
> in the future as devm_memremap_pages() is continuing to find new users
> like peer-to-peer DMA support and Linux is better off if that
> development is upstream. From a purely technical standpoint
> devm_memremap_pages() is EXPORT_SYMBOL_GPL because it hacks around
> several implementation details in the core kernel to achieve its goal,
> and it leaks new assumptions all over the kernel. It is strictly not a
> self contained interface.

Agreed with all of that.  And remember EXPORT_SYMBOL_GPL really just is
a clear expression of the authors they think these are internals.
The lack of it doesn't make it any less a derived work, we just remove
a very clear hint to users that they are poking very deeply into internals.

And with HMM they very clearly do.