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

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Message-ID: <20201202162215.GS1161629@iweiny-DESK2.sc.intel.com>
Date:   Wed, 2 Dec 2020 08:22:15 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, vbabka@...e.cz, mhocko@...e.com,
        david@...hat.com, osalvador@...e.de, dan.j.williams@...el.com,
        sashal@...nel.org, tyhicks@...ux.microsoft.com,
        iamjoonsoo.kim@....com, mike.kravetz@...cle.com,
        rostedt@...dmis.org, mingo@...hat.com, jgg@...pe.ca,
        peterz@...radead.org, mgorman@...e.de, willy@...radead.org,
        rientjes@...gle.com, jhubbard@...dia.com
Subject: Re: [PATCH 1/6] mm/gup: perform check_dax_vmas only when FS_DAX is
 enabled

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.

Ira

> +#ifdef CONFIG_FS_DAX
>  static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>  {
>  	long i;
> @@ -1586,6 +1587,12 @@ 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
>  
>  #ifdef CONFIG_CMA
>  static long check_and_migrate_cma_pages(struct mm_struct *mm,
> -- 
> 2.25.1
> 
>