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Subject: Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN
From:   John Hubbard <jhubbard@nvidia.com>
To:     Jan Kara <jack@suse.cz>
CC:     Andrew Morton <akpm@linux-foundation.org>,
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On 11/13/19 3:22 PM, John Hubbard wrote:
> On 11/13/19 2:43 AM, Jan Kara wrote:
> ...
>> How does FOLL_PIN result in grabbing (at least normal, for now) page reference?
>> I didn't find that anywhere in this patch but it is a prerequisite to
>> converting any user to pin_user_pages() interface, right?
> 
> 
> ohhh, I messed up on this intermediate patch: it doesn't quite stand alone as
> it should, as you noticed. To correct this, I can do one of the following:
> 
> a) move the new pin*() routines into the later patch 16 ("mm/gup:
> track FOLL_PIN pages"), or
> 
> b) do a temporary thing here, such as setting FOLL_GET and adding a TODO,
> within the pin*() implementations. And this switching it over to FOLL_PIN
> in patch 16.
> 
> I'm thinking (a) is less error-prone, so I'm going with that unless someone
> points out that that is stupid. :)
> 

OK, just to save anyone from wasting time reading the above: (a) is, in fact,
stupid, after all. ha. That is because pin_user_pages() is called in the 
intervening patches.
 
So anyway, I'll work out an ordering to fix it up, it's not complicated.


thanks,
-- 
John Hubbard
NVIDIA