linux-kernel - Re: [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection

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Date:   Fri, 28 Feb 2020 15:36:54 +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,
        richardw.yang@...ux.intel.com, osalvador@...e.de,
        dan.j.williams@...el.com, mhocko@...e.com, rppt@...ux.ibm.com,
        robin.murphy@....com
Subject: Re: [PATCH v2 3/7] mm/sparse.c: introduce a new function
 clear_subsection_map()

On 20.02.20 05:33, Baoquan He wrote:
> Wrap the codes 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 | 46 ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 38 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 977b47acd38d..df857ee9330c 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -726,14 +726,25 @@ 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)
> +/**
> + * clear_subsection_map - Clear subsection map of one memory region
> + *
> + * @pfn - start pfn of the memory range
> + * @nr_pages - number of pfns to add in the region
> + *
> + * This is only intended for hotplug, and clear the related subsection
> + * map inside one section.
> + *
> + * Return:
> + * * -EINVAL	- Section already deactived.
> + * * 0		- Subsection map is emptied.
> + * * 1		- Subsection map is not empty.
> + */

Less verbose please (in my preference: none and simplify return handling)

> +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;
>  	unsigned long *subsection_map = ms->usage
>  		? &ms->usage->subsection_map[0] : NULL;
>  
> @@ -744,8 +755,28 @@ 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;
> +		return -EINVAL;
> +
> +	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
>  
> +	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> +		return 0;
> +

Can we please just have a

subsection_map_empty() instead and handle that in the caller?
(you can then always return true in the !VMEMMAP variant)

I dislike the "rc" handling in the caller.

> +	return 1;
> +}
> +
> +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;
> +	int rc;
> +
> +

one superfluous empty line

> +	rc = clear_subsection_map(pfn, nr_pages);
> +	if (IS_ERR_VALUE((unsigned long)rc))

huh? "if (rc < 0)" ? or am I missing something?

> +		return;
>  	/*
>  	 * There are 3 cases to handle across two configurations
>  	 * (SPARSEMEM_VMEMMAP={y,n}):
> @@ -763,8 +794,7 @@ 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);
> -	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) {
> +	if (!rc) {
>  		unsigned long section_nr = pfn_to_section_nr(pfn);
>  
>  		/*
> @@ -786,7 +816,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  	else
>  		depopulate_section_memmap(pfn, nr_pages, altmap);
>  
> -	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> +	if (!rc)

I don't really like that handling.

Either

s/rc/section_empty/

or use a separate subsection_map_empty()

>  		ms->section_mem_map = (unsigned long)NULL;
>  }
>  
> 

Thanks!

-- 
Thanks,

David / dhildenb