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Subject: Re: [PATCH 19/19] Documentation/vm: add pin_user_pages.rst
To:     Ira Weiny <ira.weiny@intel.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
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References: <20191030224930.3990755-1-jhubbard@nvidia.com>
 <20191030224930.3990755-20-jhubbard@nvidia.com>
 <20191031234922.GM14771@iweiny-DESK2.sc.intel.com>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <85de5845-d403-dc31-4f3b-f006c4a7b2a2@nvidia.com>
Date:   Thu, 31 Oct 2019 16:53:39 -0700
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On 10/31/19 4:49 PM, Ira Weiny wrote:
> On Wed, Oct 30, 2019 at 03:49:30PM -0700, John Hubbard wrote:
>> Document the new pin_user_pages() and related calls
>> and behavior.
>>
>> Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases
>> in this documentation. (I've reworded it and expanded on it slightly.)
> 
> As I said before I think this may be better in a previous patch where you
> reference it.

Yes, I'll merge this in with patch #5 ("mm/gup: introduce pin_user_pages*()
and FOLL_PIN").

...
>> +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, that is better, I'll use that instead of the "TODO".


thanks,

John Hubbard
NVIDIA