linux-kernel - Re: [PATCH 3/6] mm/gup: make __gup_longterm

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Date:   Wed, 2 Dec 2020 19:03:04 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, mike.kravetz@...cle.com,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 3/6] mm/gup: make __gup_longterm_locked common

On Wed, Dec 2, 2020 at 1:19 PM Pavel Tatashin <pasha.tatashin@...een.com> wrote:
>
> On Wed, Dec 2, 2020 at 11:33 AM Ira Weiny <ira.weiny@...el.com> wrote:
> >
> > On Wed, Dec 02, 2020 at 08:31:45AM -0800, 'Ira Weiny' wrote:
> > > On Wed, Dec 02, 2020 at 12:23:27AM -0500, Pavel Tatashin wrote:
> > > > __gup_longterm_locked() has CMA || FS_DAX version and a common stub
> > > > version. In the preparation of prohibiting longterm pinning of pages from
> > > > movable zone make the CMA || FS_DAX version common, and delete the stub
> > > > version.
> > > >
> > > > Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> > > > ---
> > > >  mm/gup.c | 13 -------------
> > > >  1 file changed, 13 deletions(-)
> > > >
> > > > diff --git a/mm/gup.c b/mm/gup.c
> > > > index 3a76c005a3e2..0e2de888a8b0 100644
> > > > --- a/mm/gup.c
> > > > +++ b/mm/gup.c
> > > > @@ -1567,7 +1567,6 @@ struct page *get_dump_page(unsigned long addr)
> > > >  }
> > > >  #endif /* CONFIG_ELF_CORE */
> > > >
> > > > -#if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
> > > >  #ifdef CONFIG_FS_DAX
> > > >  static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
> > > >  {
> > > > @@ -1757,18 +1756,6 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> > > >             kfree(vmas_tmp);
> > > >     return rc;
> > > >  }
> > >
> > > Isn't this going to potentially allocate vmas_tmp only to not need it when
> > > !FS_DAX and !CMA?
> >
> > To clarify, when FOLL_LONGTERM is set...
>
> Yes, this is the case. We need that because once migration is checked
> for all allocations, not only CMA, we need vmas_tmp for all cases.

A slight correction, we only need vmas_tmp for check_dax_vmas().
Potentially, we could wrap vmas_tmp allocation in a #ifdef for FS_DAX,
but I do not think this is really needed.

Pasha

>
> Pasha
>
> >
> > IRa
> >
> > >
> > > Ira
> > >
> > > > -#else /* !CONFIG_FS_DAX && !CONFIG_CMA */
> > > > -static __always_inline long __gup_longterm_locked(struct mm_struct *mm,
> > > > -                                             unsigned long start,
> > > > -                                             unsigned long nr_pages,
> > > > -                                             struct page **pages,
> > > > -                                             struct vm_area_struct **vmas,
> > > > -                                             unsigned int flags)
> > > > -{
> > > > -   return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
> > > > -                                  NULL, flags);
> > > > -}
> > > > -#endif /* CONFIG_FS_DAX || CONFIG_CMA */
> > > >
> > > >  static bool is_valid_gup_flags(unsigned int gup_flags)
> > > >  {
> > > > --
> > > > 2.25.1
> > > >
> > > >
> > >