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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Mon, 25 Mar 2019 09:45:12 -0700
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Subject: Re: [RESEND 1/7] mm/gup: Replace get_user_pages_longterm() with FOLL_LONGTERM
To:     Ira Weiny <ira.weiny@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        "David S. Miller" <davem@davemloft.net>,
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        Rich Felker <dalias@libc.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
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        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Ralf Baechle <ralf@linux-mips.org>,
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On Mon, Mar 25, 2019 at 7:21 AM Ira Weiny <ira.weiny@intel.com> wrote:
[..]
> > > @@ -1268,10 +1246,14 @@ static long check_and_migrate_cma_pages(unsigned long start, long nr_pages,
> > >                                 putback_movable_pages(&cma_page_list);
> > >                 }
> > >                 /*
> > > -                * We did migrate all the pages, Try to get the page references again
> > > -                * migrating any new CMA pages which we failed to isolate earlier.
> > > +                * We did migrate all the pages, Try to get the page references
> > > +                * again migrating any new CMA pages which we failed to isolate
> > > +                * earlier.
> > >                  */
> > > -               nr_pages = get_user_pages(start, nr_pages, gup_flags, pages, vmas);
> > > +               nr_pages = __get_user_pages_locked(tsk, mm, start, nr_pages,
> > > +                                                  pages, vmas, NULL,
> > > +                                                  gup_flags);
> > > +
> >
> > Why did this need to change to __get_user_pages_locked?
>
> __get_uer_pages_locked() is now the "internal call" for get_user_pages.
>
> Technically it did not _have_ to change but there is no need to call
> get_user_pages() again because the FOLL_TOUCH flags is already set.  Also this
> call then matches the __get_user_pages_locked() which was called on the pages
> we migrated from.  Mostly this keeps the code "symmetrical" in that we called
> __get_user_pages_locked() on the pages we are migrating from and the same call
> on the pages we migrated to.
>
> While the change here looks funny I think the final code is better.

Agree, but I think that either needs to be noted in the changelog so
it's not a surprise, or moved to a follow-on cleanup patch.