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Date:   Wed, 12 Feb 2020 19:26:41 +0800
From:   Baoquan He <bhe@redhat.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, dan.j.williams@intel.com,
        richardw.yang@linux.intel.com
Subject: Re: [PATCH 3/7] mm/sparse.c: only use subsection map in VMEMMAP case
Message-ID: <20200212112641.GJ26758@MiWiFi-R3L-srv>
References: <20200209104826.3385-1-bhe@redhat.com>
 <20200209104826.3385-4-bhe@redhat.com>
 <be1625c4-6875-cfba-9894-f9c148cfe4e7@redhat.com>
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On 02/11/20 at 03:43pm, David Hildenbrand wrote:
> 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@redhat.com>
> > ---
> >  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 :)

OK, I did it in the first place. Later I think putting all subsectin
related handling into one place makes code look better. Now I understand
it may make patch format messy. I will adjust the place to make
reviewing easier. Thanks for your great suggestion.