linux-kernel - Re: [PATCH 1/6] mm/gup: perform check_dax_vmas only when FS

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Date:   Wed, 2 Dec 2020 13:15:04 -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 1/6] mm/gup: perform check_dax_vmas only when FS_DAX is enabled

On Wed, Dec 2, 2020 at 11:22 AM Ira Weiny <ira.weiny@...el.com> wrote:
>
> On Wed, Dec 02, 2020 at 12:23:25AM -0500, Pavel Tatashin wrote:
> > There is no need to check_dax_vmas() and run through the npage loop of
> > pinned pages if FS_DAX is not enabled.
> >
> > Add a stub check_dax_vmas() function for no-FS_DAX case.
>
> This looks like a good idea.
>
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> > ---
> >  mm/gup.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 98eb8e6d2609..cdb8b9eeb016 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1568,6 +1568,7 @@ struct page *get_dump_page(unsigned long addr)
> >  #endif /* CONFIG_ELF_CORE */
> >
> >  #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
>
> In addition, I think it would make a lot of sense to clean up this config as
> well like this:
>
> 08:20:10 > git di
> diff --git a/mm/gup.c b/mm/gup.c
> index 102877ed77a4..92cfda220aeb 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1567,7 +1567,7 @@ 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)
>  {
>         long i;
> @@ -1586,6 +1586,12 @@ static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>         }
>         return false;
>  }
> +#else
> +static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
> +{
> +       return false;
> +}
> +#endif /* CONFIG_FS_DAX */
>
>  #ifdef CONFIG_CMA
>  static long check_and_migrate_cma_pages(struct mm_struct *mm,
> @@ -1691,6 +1697,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
>  }
>  #endif /* CONFIG_CMA */
>
> +#if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
>  /*
>   * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
>   * allows us to process the FOLL_LONGTERM flag.
>
>
> That makes it more clear what is going on with __gup_longterm_locked() and
> places both CMA and FS_DAX code within their own blocks.

Hi Ira,

Thank you for your comments. I think the end result of what you are
suggesting is the same for this series when __gup_longterm_locked is
made common. " #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)"
mess is removed in that patch.

Pasha