linux-kernel - Re: [RFC] mm/gup.c: Use gup_flags as parameter instead of passing write flag

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Message-ID: <CAFqt6zbcn5kEbtY1fod4yy_PETKX8zVM2NjsY0HHyOixiu2q4w@mail.gmail.com>
Date:   Tue, 19 May 2020 02:14:01 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm/gup.c: Use gup_flags as parameter instead of passing
 write flag

On Tue 19 May, 2020, 1:47 AM Matthew Wilcox, <willy@...radead.org> wrote:
>
> On Tue, May 19, 2020 at 01:28:23AM +0530, Souptick Joarder wrote:
> > The idea is to get rid of write parameter. Instead caller will pass
> > FOLL_WRITE to __get_user_pages_fast(). This will not change any
> > functionality of the API. Once it is upstream all the callers will
> > be changed to pass FOLL_WRITE.
>
> Uhh ... until you change all the callers, haven't you just broken all
> the callers?

All the callers have called the API with either 1 or 0.  I think, it's
not going to break
any of the callers.

>
> > -int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> > -                       struct page **pages)
> > +int __get_user_pages_fast(unsigned long start, int nr_pages,
> > +                     unsigned int gup_flags, struct page **pages)
> >  {
> >       unsigned long len, end;
> >       unsigned long flags;
> > @@ -2685,10 +2692,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> >        * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
> >        * because gup fast is always a "pin with a +1 page refcount" request.
> >        */
> > -     unsigned int gup_flags = FOLL_GET;
> > -
> > -     if (write)
> > -             gup_flags |= FOLL_WRITE;
> > +     gup_flags |= FOLL_GET;