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Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
To:     Jerome Glisse <jglisse@redhat.com>
CC:     Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
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From:   John Hubbard <jhubbard@nvidia.com>
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On 12/12/18 2:14 PM, Jerome Glisse wrote:
> On Wed, Dec 12, 2018 at 02:11:58PM -0800, John Hubbard wrote:
>> On 12/12/18 2:04 PM, Jerome Glisse wrote:
>>> On Wed, Dec 12, 2018 at 01:56:00PM -0800, John Hubbard wrote:
>>>> On 12/12/18 1:30 PM, Jerome Glisse wrote:
>>>>> On Wed, Dec 12, 2018 at 08:27:35AM -0800, Dan Williams wrote:
>>>>>> On Wed, Dec 12, 2018 at 7:03 AM Jerome Glisse <jglisse@redhat.com> wrote:
>>>>>>>
>>>>>>> On Mon, Dec 10, 2018 at 11:28:46AM +0100, Jan Kara wrote:
>>>>>>>> On Fri 07-12-18 21:24:46, Jerome Glisse wrote:
[...]
>>>
>>>>>     Patch 1: register mmu notifier
>>>>>     Patch 2: listen to MMU_NOTIFY_TRUNCATE and MMU_NOTIFY_UNMAP
>>>>>              when that happens update the device page table or
>>>>>              usage to point to a crappy page and do put_user_page
>>>>>              on all previously held page
>>>>
>>>> Minor point, this sequence should be done within a wrapper around existing 
>>>> get_user_pages(), such as get_user_pages_revokable() or something.
>>>
>>> No we want to teach everyone to abide by the rules, if we add yet another
>>> GUP function prototype people will use the one where they don;t have to
>>> say they abide by the rules. It is time we advertise the fact that GUP
>>> should not be use willy nilly for anything without worrying about the
>>> implication it has :)
>>
>> Well, the best way to do that is to provide a named function call that 
>> implements the rules. That also makes it easy to grep around and see which
>> call sites still need upgrades, and which don't.
>>
>>>
>>> So i would rather see a consolidation in the number of GUP prototype we
>>> have than yet another one.
>>
>> We could eventually get rid of the older GUP prototypes, once we're done
>> converting. Having a new, named function call will *without question* make
>> the call site conversion go much easier, and the end result is also better:
>> the common code is in a central function, rather than being at all the call
>> sites.
>>
> 
> Then last patch in the patchset must remove all GUP prototype except
> ones with the right API :)
> 

Yes, exactly.


thanks,
-- 
John Hubbard
NVIDIA