netdev - Re: [PATCH 19/19] Documentation/vm: add pin_user

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Message-ID: <8f92713c-7df8-9463-93f2-40967eba27b5@nvidia.com>
Date:   Thu, 31 Oct 2019 17:48:36 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>
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>,
        Christoph Hellwig <hch@...radead.org>,
        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>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        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>
Subject: Re: [PATCH 19/19] Documentation/vm: add pin_user_pages.rst

On 10/31/19 4:49 PM, Ira Weiny wrote:
> On Wed, Oct 30, 2019 at 03:49:30PM -0700, John Hubbard wrote:
...
>> +TODO: There is also a special case when the pages are DAX pages: in addition to
>> +the above flags, the caller needs something like a layout lease on the
>> +associated file. This is yet to be implemented. When it is implemented, it's
>> +expected that the lease will be a prerequisite to setting FOLL_LONGTERM.
> 
> For now we probably want to leave this note out until we figure out how this is
> going to work.  Best to say something like:
> 
> Some pages, such as DAX pages, can't be pinned with longterm pins and will
> fail.
> 

OK, I have this wording queued up for the v2 patch:

NOTE: Some pages, such as DAX pages, cannot be pinned with longterm pins. That's
because DAX pages do not have a separate page cache, and so "pinning" implies
locking down file system blocks, which is not (yet) supported in that way.


thanks,

John Hubbard
NVIDIA