linux-kernel - Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function clear_subsection

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Date:   Mon, 9 Mar 2020 09:59:57 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, mhocko@...e.com,
        richardw.yang@...ux.intel.com, dan.j.williams@...el.com,
        osalvador@...e.de, rppt@...ux.ibm.com
Subject: Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function
 clear_subsection_map()

On 07.03.20 09:42, Baoquan He wrote:
> Factor out the code which clear subsection map of one memory region from
> section_deactivate() into clear_subsection_map().
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/sparse.c | 31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index e37c0abcdc89..d9dcd58d5c1d 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -726,15 +726,11 @@ static void free_map_bootmem(struct page *memmap)
>  }
>  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>  
> -static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> -		struct vmem_altmap *altmap)
> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
>  {
>  	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
>  	DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
>  	struct mem_section *ms = __pfn_to_section(pfn);
> -	bool section_is_early = early_section(ms);
> -	struct page *memmap = NULL;
> -	bool empty = false;
>  	unsigned long *subsection_map = ms->usage
>  		? &ms->usage->subsection_map[0] : NULL;
>  
> @@ -745,8 +741,31 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  	if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
>  				"section already deactivated (%#lx + %ld)\n",
>  				pfn, nr_pages))
> +		return -EINVAL;
> +
> +	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> +

Nit: I'd drop this line.

> +	return 0;
> +}
> +
> +static bool is_subsection_map_empty(struct mem_section *ms)
> +{
> +	return bitmap_empty(&ms->usage->subsection_map[0],
> +			    SUBSECTIONS_PER_SECTION);
> +}
> +
> +static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> +		struct vmem_altmap *altmap)
> +{
> +	struct mem_section *ms = __pfn_to_section(pfn);
> +	bool section_is_early = early_section(ms);
> +	struct page *memmap = NULL;
> +	bool empty = false;

Nit: No need to initialize empty.

> +
> +	if (clear_subsection_map(pfn, nr_pages))
>  		return;
>  

Nit: I'd drop this empty line.

> +	empty = is_subsection_map_empty(ms);
>  	/*
>  	 * There are 3 cases to handle across two configurations
>  	 * (SPARSEMEM_VMEMMAP={y,n}):
> @@ -764,8 +783,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  	 *
>  	 * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
>  	 */
> -	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> -	empty = bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);

I do wonder why you moved this up the comment?

>  	if (empty) {
>  		unsigned long section_nr = pfn_to_section_nr(pfn);
>  
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb