Re: [Linux-kernel-mentees][PATCH v6 1/2] sgi-gru: Convert put_page() to put_user_page*()

Michal Hocko
2019-08-20T08:18:25Z

On Mon 19-08-19 12:30:18, John Hubbard wrote:
> On 8/19/19 12:06 PM, Bharath Vedartham wrote:
> > On Mon, Aug 19, 2019 at 07:56:11AM -0500, Dimitri Sivanich wrote:
> > > Reviewed-by: Dimitri Sivanich <sivanich@hpe.com>
> > Thanks!
> >
> > John, would you like to take this patch into your miscellaneous
> > conversions patch set?
> >
>
> (+Andrew and Michal, so they know where all this is going.)
>
> Sure, although that conversion series [1] is on a brief hold, because
> there are additional conversions desired, and the API is still under
> discussion. Also, reading between the lines of Michal's response [2]
> about it, I think people would prefer that the next revision include
> the following, for each conversion site:
>
> Conversion of gup/put_page sites:
>
> Before:
>
> get_user_pages(...);
> ...
> for each page:
> put_page();
>
> After:
>
> gup_flags |= FOLL_PIN; (maybe FOLL_LONGTERM in some cases)
> vaddr_pin_user_pages(...gup_flags...)

I was hoping that FOLL_PIN would be handled by vaddr_pin_user_pages.

> ...
> vaddr_unpin_user_pages(); /* which invokes put_user_page() */
>
> Fortunately, it's not harmful for the simpler conversion from put_page()
> to put_user_page() to happen first, and in fact those have usually led
> to simplifications, paving the way to make it easier to call
> vaddr_unpin_user_pages(), once it's ready. (And showing exactly what
> to convert, too.)

If that makes the later conversion easier then no real objections from
me. Assuming that the current put_user_page conversions are correct of
course (I have the mlock one and potentials that falls into the same
category in mind).
--
Michal Hocko
SUSE Labs