linux-kernel - Re: [RESEND 1/7] mm/gup: Replace get_user_pages_longterm() with FOLL

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Date:   Mon, 25 Mar 2019 01:46:14 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rich Felker <dalias@...c.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Michal Hocko <mhocko@...nel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh <linux-sh@...r.kernel.org>, sparclinux@...r.kernel.org,
        linux-rdma <linux-rdma@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RESEND 1/7] mm/gup: Replace get_user_pages_longterm() with
 FOLL_LONGTERM

On Mon, Mar 25, 2019 at 09:45:12AM -0700, Dan Williams wrote:
> On Mon, Mar 25, 2019 at 7:21 AM Ira Weiny <ira.weiny@...el.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.
> 

Can do...

Thanks!
Ira