netdev - Re: [PATCH v12 04/22] mm: devmap: refactor 1-based refcounting for ZONE

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Date:   Thu, 16 Jan 2020 12:30:26 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <kvm@...r.kernel.org>,
        <linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <netdev@...r.kernel.org>,
        <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v12 04/22] mm: devmap: refactor 1-based refcounting for
 ZONE_DEVICE pages

On 1/16/20 1:37 AM, Christoph Hellwig wrote:
> On Wed, Jan 15, 2020 at 01:19:41PM -0800, John Hubbard wrote:
>> On 1/15/20 7:23 AM, Christoph Hellwig wrote:
>> ...
>>>
>>> I'm really not sold on this scheme.  Note that I think it is
>>> particularly bad, but it also doesn't seem any better than what
>>> we had before, and it introduced quite a bit more code.
>>>
>>
>> Hi Christoph,
>>
>> All by itself, yes. But the very next patch (which needs a little
>> rework for other reasons, so not included here) needs to reuse some of
>> these functions within __unpin_devmap_managed_user_page():
> 
> Well, then combine it with the series that actually does the change.


OK, that makes sense. I just double-checked with a quick test run, that it
doesn't have dependencies with the rest of this series, and it came out clean,
so:

Andrew, could you please remove just this one patch from mmotm and linux-next?


> 
> Also my vaguely recollection is that we had some idea on how to get rid
> of the off by one refcounting for the zone device pages, which would be
> a much better outcome.
> 

Yes, I recall that Dan Williams mentioned it, but I don't think he provided
any details yet.


thanks,
-- 
John Hubbard
NVIDIA