Re: [PATCH 3/7] mm/sparse.c: only use subsection map in VMEMMAP case

[David Hildenbrand]

On 09.02.20 11:48, Baoquan He wrote:
> Currently, subsection map is used when SPARSEMEM is enabled, including
> VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not
> supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary
> and misleading. Let's adjust code to only allow subsection map being
> used in SPARSEMEM|VMEMMAP case.
> 
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
>  include/linux/mmzone.h |   2 +
>  mm/sparse.c            | 231 ++++++++++++++++++++++-------------------
>  2 files changed, 124 insertions(+), 109 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 462f6873905a..fc0de3a9a51e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1185,7 +1185,9 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
>  #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)
>  
>  struct mem_section_usage {
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
>  	DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
> +#endif
>  	/* See declaration of similar field in struct zone */
>  	unsigned long pageblock_flags[0];
>  };
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 696f6b9f706e..cf55d272d0a9 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -209,41 +209,6 @@ static inline unsigned long first_present_section_nr(void)
>  	return next_present_section_nr(-1);
>  }
>  
> -static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> -		unsigned long nr_pages)
> -{
> -	int idx = subsection_map_index(pfn);
> -	int end = subsection_map_index(pfn + nr_pages - 1);
> -
> -	bitmap_set(map, idx, end - idx + 1);
> -}
> -
> -void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> -{
> -	int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> -	unsigned long nr, start_sec = pfn_to_section_nr(pfn);
> -
> -	if (!nr_pages)
> -		return;
> -
> -	for (nr = start_sec; nr <= end_sec; nr++) {
> -		struct mem_section *ms;
> -		unsigned long pfns;
> -
> -		pfns = min(nr_pages, PAGES_PER_SECTION
> -				- (pfn & ~PAGE_SECTION_MASK));
> -		ms = __nr_to_section(nr);
> -		subsection_mask_set(ms->usage->subsection_map, pfn, pfns);
> -
> -		pr_debug("%s: sec: %lu pfns: %lu set(%d, %d)\n", __func__, nr,
> -				pfns, subsection_map_index(pfn),
> -				subsection_map_index(pfn + pfns - 1));
> -
> -		pfn += pfns;
> -		nr_pages -= pfns;
> -	}
> -}
> -
>  /* Record a memory area against a node. */
>  void __init memory_present(int nid, unsigned long start, unsigned long end)
>  {
> @@ -432,12 +397,134 @@ static unsigned long __init section_map_size(void)
>  	return ALIGN(sizeof(struct page) * PAGES_PER_SECTION, PMD_SIZE);
>  }
>  
> +static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> +		unsigned long nr_pages)
> +{
> +	int idx = subsection_map_index(pfn);
> +	int end = subsection_map_index(pfn + nr_pages - 1);
> +
> +	bitmap_set(map, idx, end - idx + 1);
> +}
> +
> +void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> +{
> +	int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> +	unsigned long nr, start_sec = pfn_to_section_nr(pfn);
> +
> +	if (!nr_pages)
> +		return;
> +
> +	for (nr = start_sec; nr <= end_sec; nr++) {
> +		struct mem_section *ms;
> +		unsigned long pfns;
> +
> +		pfns = min(nr_pages, PAGES_PER_SECTION
> +				- (pfn & ~PAGE_SECTION_MASK));
> +		ms = __nr_to_section(nr);
> +		subsection_mask_set(ms->usage->subsection_map, pfn, pfns);
> +
> +		pr_debug("%s: sec: %lu pfns: %lu set(%d, %d)\n", __func__, nr,
> +				pfns, subsection_map_index(pfn),
> +				subsection_map_index(pfn + pfns - 1));
> +
> +		pfn += pfns;
> +		nr_pages -= pfns;
> +	}
> +}
> +
> +/**
> + * 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.
> + */
> +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);
> +	unsigned long *subsection_map = ms->usage
> +		? &ms->usage->subsection_map[0] : NULL;
> +
> +	subsection_mask_set(map, pfn, nr_pages);
> +	if (subsection_map)
> +		bitmap_and(tmp, map, subsection_map, SUBSECTIONS_PER_SECTION);
> +
> +	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);
> +
> +	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> +		return 0;
> +
> +	return 1;
> +}
> +
> +/**
> + * fill_subsection_map - fill subsection map of a memory region
> + * @pfn - start pfn of the memory range
> + * @nr_pages - number of pfns to add in the region
> + *
> + * This clears the related subsection map inside one section, and only
> + * intended for hotplug.
> + *
> + * Return:
> + * * 0		- On success.
> + * * -EINVAL	- Invalid memory region.
> + * * -EEXIST	- Subsection map has been set.
> + */
> +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> +	struct mem_section *ms = __pfn_to_section(pfn);
> +	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> +	unsigned long *subsection_map;
> +	int rc = 0;
> +
> +	subsection_mask_set(map, pfn, nr_pages);
> +
> +	subsection_map = &ms->usage->subsection_map[0];
> +
> +	if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
> +		rc = -EINVAL;
> +	else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION))
> +		rc = -EEXIST;
> +	else
> +		bitmap_or(subsection_map, map, subsection_map,
> +				SUBSECTIONS_PER_SECTION);
> +
> +	return rc;
> +}
> +
>  #else
>  static unsigned long __init section_map_size(void)
>  {
>  	return PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION);
>  }
>  
> +void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> +{
> +}
> +
> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> +	return 0;
> +}
> +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> +	return 0;
> +}
> +
>  struct page __init *__populate_section_memmap(unsigned long pfn,
>  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
>  {
> @@ -726,45 +813,6 @@ static void free_map_bootmem(struct page *memmap)
>  }
>  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>  
> -/**
> - * 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.
> - */
> -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);
> -	unsigned long *subsection_map = ms->usage
> -		? &ms->usage->subsection_map[0] : NULL;
> -
> -	subsection_mask_set(map, pfn, nr_pages);
> -	if (subsection_map)
> -		bitmap_and(tmp, map, subsection_map, SUBSECTIONS_PER_SECTION);
> -
> -	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);
> -
> -	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> -		return 0;
> -
> -	return 1;
> -}
> -
>  static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  		struct vmem_altmap *altmap)
>  {
> @@ -818,41 +866,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  		depopulate_section_memmap(pfn, nr_pages, altmap);
>  }
>  
> -/**
> - * fill_subsection_map - fill subsection map of a memory region
> - * @pfn - start pfn of the memory range
> - * @nr_pages - number of pfns to add in the region
> - *
> - * This clears the related subsection map inside one section, and only
> - * intended for hotplug.
> - *
> - * Return:
> - * * 0		- On success.
> - * * -EINVAL	- Invalid memory region.
> - * * -EEXIST	- Subsection map has been set.
> - */
> -static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> -{
> -	struct mem_section *ms = __pfn_to_section(pfn);
> -	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> -	unsigned long *subsection_map;
> -	int rc = 0;
> -
> -	subsection_mask_set(map, pfn, nr_pages);
> -
> -	subsection_map = &ms->usage->subsection_map[0];
> -
> -	if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
> -		rc = -EINVAL;
> -	else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION))
> -		rc = -EEXIST;
> -	else
> -		bitmap_or(subsection_map, map, subsection_map,
> -				SUBSECTIONS_PER_SECTION);
> -
> -	return rc;
> -}
> -
>  static struct page * __meminit section_activate(int nid, unsigned long pfn,
>  		unsigned long nr_pages, struct vmem_altmap *altmap)
>  {
> 

I'd prefer adding more ifdefs to avoid heavy code movement. Would make
it much easier to review :)

-- 
Thanks,

David / dhildenb