[v8,01/12] mm/sparsemem: Introduce struct mem_section_usage
diff mbox series

Message ID 155718597192.130019.7128788290111464258.stgit@dwillia2-desk3.amr.corp.intel.com
State New
Headers show
Series
  • mm: Sub-section memory hotplug support
Related show

Commit Message

Dan Williams May 6, 2019, 11:39 p.m. UTC
Towards enabling memory hotplug to track partial population of a
section, introduce 'struct mem_section_usage'.

A pointer to a 'struct mem_section_usage' instance replaces the existing
pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
house a new 'subsection_map' bitmap.  The new bitmap enables the memory
hot{plug,remove} implementation to act on incremental sub-divisions of a
section.

The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no
larger than a single 'unsigned long' on the major architectures.
Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to
override the default PMD_SHIFT. Note that PowerPC needs to use
ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant
expression on PowerPC.

The primary motivation for this functionality is to support platforms
that mix "System RAM" and "Persistent Memory" within a single section,
or multiple PMEM ranges with different mapping lifetimes within a single
section. The section restriction for hotplug has caused an ongoing saga
of hacks and bugs for devm_memremap_pages() users.

Beyond the fixups to teach existing paths how to retrieve the 'usemap'
from a section, and updates to usemap allocation path, there are no
expected behavior changes.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/powerpc/include/asm/sparsemem.h |    3 +
 include/linux/mmzone.h               |   48 +++++++++++++++++++-
 mm/memory_hotplug.c                  |   18 ++++----
 mm/page_alloc.c                      |    2 -
 mm/sparse.c                          |   81 +++++++++++++++++-----------------
 5 files changed, 99 insertions(+), 53 deletions(-)

Comments

Oscar Salvador May 10, 2019, 1:30 p.m. UTC | #1
On 2019-05-07 01:39, Dan Williams wrote:
> Towards enabling memory hotplug to track partial population of a
> section, introduce 'struct mem_section_usage'.
> 
> A pointer to a 'struct mem_section_usage' instance replaces the 
> existing
> pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
> 'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
> house a new 'subsection_map' bitmap.  The new bitmap enables the memory
> hot{plug,remove} implementation to act on incremental sub-divisions of 
> a
> section.
> 
> The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no
> larger than a single 'unsigned long' on the major architectures.
> Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to
> override the default PMD_SHIFT. Note that PowerPC needs to use
> ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant
> expression on PowerPC.
> 
> The primary motivation for this functionality is to support platforms
> that mix "System RAM" and "Persistent Memory" within a single section,
> or multiple PMEM ranges with different mapping lifetimes within a 
> single
> section. The section restriction for hotplug has caused an ongoing saga
> of hacks and bugs for devm_memremap_pages() users.
> 
> Beyond the fixups to teach existing paths how to retrieve the 'usemap'
> from a section, and updates to usemap allocation path, there are no
> expected behavior changes.
> 
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  arch/powerpc/include/asm/sparsemem.h |    3 +
>  include/linux/mmzone.h               |   48 +++++++++++++++++++-
>  mm/memory_hotplug.c                  |   18 ++++----
>  mm/page_alloc.c                      |    2 -
>  mm/sparse.c                          |   81 
> +++++++++++++++++-----------------
>  5 files changed, 99 insertions(+), 53 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/sparsemem.h
> b/arch/powerpc/include/asm/sparsemem.h
> index 3192d454a733..1aa3c9303bf8 100644
> --- a/arch/powerpc/include/asm/sparsemem.h
> +++ b/arch/powerpc/include/asm/sparsemem.h
> @@ -10,6 +10,9 @@
>   */
>  #define SECTION_SIZE_BITS       24
> 
> +/* Reflect the largest possible PMD-size as the subsection-size 
> constant */
> +#define ARCH_SUBSECTION_SHIFT 24
> +

I guess this is done because PMD_SHIFT is defined at runtime rather at 
compile time,
right?


>  #endif /* CONFIG_SPARSEMEM */
> 
>  #ifdef CONFIG_MEMORY_HOTPLUG
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 70394cabaf4e..ef8d878079f9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1160,6 +1160,44 @@ static inline unsigned long
> section_nr_to_pfn(unsigned long sec)
>  #define SECTION_ALIGN_UP(pfn)	(((pfn) + PAGES_PER_SECTION - 1) &
> PAGE_SECTION_MASK)
>  #define SECTION_ALIGN_DOWN(pfn)	((pfn) & PAGE_SECTION_MASK)
> 
> +/*
> + * SUBSECTION_SHIFT must be constant since it is used to declare
> + * subsection_map and related bitmaps without triggering the 
> generation
> + * of variable-length arrays. The most natural size for a subsection 
> is
> + * a PMD-page. For architectures that do not have a constant PMD-size
> + * ARCH_SUBSECTION_SHIFT can be set to a constant max size, or 
> otherwise
> + * fallback to 2MB.
> + */
> +#if defined(ARCH_SUBSECTION_SHIFT)
> +#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
> +#elif defined(PMD_SHIFT)
> +#define SUBSECTION_SHIFT (PMD_SHIFT)
> +#else
> +/*
> + * Memory hotplug enabled platforms avoid this default because they
> + * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant, 
> but
> + * this is kept as a backstop to allow compilation on
> + * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
> + */
> +#define SUBSECTION_SHIFT 21
> +#endif
> +
> +#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
> +#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
> +#define PAGE_SUBSECTION_MASK ((~(PAGES_PER_SUBSECTION-1)))
> +
> +#if SUBSECTION_SHIFT > SECTION_SIZE_BITS
> +#error Subsection size exceeds section size
> +#else
> +#define SUBSECTIONS_PER_SECTION (1UL << (SECTION_SIZE_BITS - 
> SUBSECTION_SHIFT))
> +#endif

On powerpc, SUBSECTIONS_PER_SECTION will equal 1 (so one big section), 
is that to be expected?
Will subsection_map_init handle this right?
Dan Williams May 10, 2019, 7:38 p.m. UTC | #2
On Fri, May 10, 2019 at 6:30 AM <osalvador@suse.de> wrote:
>
> On 2019-05-07 01:39, Dan Williams wrote:
> > Towards enabling memory hotplug to track partial population of a
> > section, introduce 'struct mem_section_usage'.
> >
> > A pointer to a 'struct mem_section_usage' instance replaces the
> > existing
> > pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
> > 'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
> > house a new 'subsection_map' bitmap.  The new bitmap enables the memory
> > hot{plug,remove} implementation to act on incremental sub-divisions of
> > a
> > section.
> >
> > The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no
> > larger than a single 'unsigned long' on the major architectures.
> > Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to
> > override the default PMD_SHIFT. Note that PowerPC needs to use
> > ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant
> > expression on PowerPC.
> >
> > The primary motivation for this functionality is to support platforms
> > that mix "System RAM" and "Persistent Memory" within a single section,
> > or multiple PMEM ranges with different mapping lifetimes within a
> > single
> > section. The section restriction for hotplug has caused an ongoing saga
> > of hacks and bugs for devm_memremap_pages() users.
> >
> > Beyond the fixups to teach existing paths how to retrieve the 'usemap'
> > from a section, and updates to usemap allocation path, there are no
> > expected behavior changes.
> >
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Logan Gunthorpe <logang@deltatee.com>
> > Cc: Oscar Salvador <osalvador@suse.de>
> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> >  arch/powerpc/include/asm/sparsemem.h |    3 +
> >  include/linux/mmzone.h               |   48 +++++++++++++++++++-
> >  mm/memory_hotplug.c                  |   18 ++++----
> >  mm/page_alloc.c                      |    2 -
> >  mm/sparse.c                          |   81
> > +++++++++++++++++-----------------
> >  5 files changed, 99 insertions(+), 53 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/sparsemem.h
> > b/arch/powerpc/include/asm/sparsemem.h
> > index 3192d454a733..1aa3c9303bf8 100644
> > --- a/arch/powerpc/include/asm/sparsemem.h
> > +++ b/arch/powerpc/include/asm/sparsemem.h
> > @@ -10,6 +10,9 @@
> >   */
> >  #define SECTION_SIZE_BITS       24
> >
> > +/* Reflect the largest possible PMD-size as the subsection-size
> > constant */
> > +#define ARCH_SUBSECTION_SHIFT 24
> > +
>
> I guess this is done because PMD_SHIFT is defined at runtime rather at
> compile time,
> right?

Correct, PowerPC has:

    #define PMD_SHIFT (PAGE_SHIFT + PTE_INDEX_SIZE)
    #define PTE_INDEX_SIZE  __pte_index_size

...where __pte_index_size is variable established at kernel init time.

> >  #endif /* CONFIG_SPARSEMEM */
> >
> >  #ifdef CONFIG_MEMORY_HOTPLUG
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index 70394cabaf4e..ef8d878079f9 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1160,6 +1160,44 @@ static inline unsigned long
> > section_nr_to_pfn(unsigned long sec)
> >  #define SECTION_ALIGN_UP(pfn)        (((pfn) + PAGES_PER_SECTION - 1) &
> > PAGE_SECTION_MASK)
> >  #define SECTION_ALIGN_DOWN(pfn)      ((pfn) & PAGE_SECTION_MASK)
> >
> > +/*
> > + * SUBSECTION_SHIFT must be constant since it is used to declare
> > + * subsection_map and related bitmaps without triggering the
> > generation
> > + * of variable-length arrays. The most natural size for a subsection
> > is
> > + * a PMD-page. For architectures that do not have a constant PMD-size
> > + * ARCH_SUBSECTION_SHIFT can be set to a constant max size, or
> > otherwise
> > + * fallback to 2MB.
> > + */
> > +#if defined(ARCH_SUBSECTION_SHIFT)
> > +#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
> > +#elif defined(PMD_SHIFT)
> > +#define SUBSECTION_SHIFT (PMD_SHIFT)
> > +#else
> > +/*
> > + * Memory hotplug enabled platforms avoid this default because they
> > + * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant,
> > but
> > + * this is kept as a backstop to allow compilation on
> > + * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
> > + */
> > +#define SUBSECTION_SHIFT 21
> > +#endif
> > +
> > +#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
> > +#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
> > +#define PAGE_SUBSECTION_MASK ((~(PAGES_PER_SUBSECTION-1)))
> > +
> > +#if SUBSECTION_SHIFT > SECTION_SIZE_BITS
> > +#error Subsection size exceeds section size
> > +#else
> > +#define SUBSECTIONS_PER_SECTION (1UL << (SECTION_SIZE_BITS -
> > SUBSECTION_SHIFT))
> > +#endif
>
> On powerpc, SUBSECTIONS_PER_SECTION will equal 1 (so one big section),
> is that to be expected?

Yes, it turns out that PowerPC has no real need for subsection support
since they were already using small 16MB sections from day one.

> Will subsection_map_init handle this right?

Yes, should work as subsection_map_index() will always return 0. Which
means that 'end' will always be 0:

    pfns = min(nr_pages, PAGES_PER_SECTION
        - (pfn & ~PAGE_SECTION_MASK));
    end = subsection_map_index(pfn + pfns - 1);

...and then the bitmap manipulation:

    bitmap_set(ms->usage->subsection_map, idx, end - idx + 1);

...will only ever set bit0.

Patch
diff mbox series

diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
index 3192d454a733..1aa3c9303bf8 100644
--- a/arch/powerpc/include/asm/sparsemem.h
+++ b/arch/powerpc/include/asm/sparsemem.h
@@ -10,6 +10,9 @@ 
  */
 #define SECTION_SIZE_BITS       24
 
+/* Reflect the largest possible PMD-size as the subsection-size constant */
+#define ARCH_SUBSECTION_SHIFT 24
+
 #endif /* CONFIG_SPARSEMEM */
 
 #ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 70394cabaf4e..ef8d878079f9 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1160,6 +1160,44 @@  static inline unsigned long section_nr_to_pfn(unsigned long sec)
 #define SECTION_ALIGN_UP(pfn)	(((pfn) + PAGES_PER_SECTION - 1) & PAGE_SECTION_MASK)
 #define SECTION_ALIGN_DOWN(pfn)	((pfn) & PAGE_SECTION_MASK)
 
+/*
+ * SUBSECTION_SHIFT must be constant since it is used to declare
+ * subsection_map and related bitmaps without triggering the generation
+ * of variable-length arrays. The most natural size for a subsection is
+ * a PMD-page. For architectures that do not have a constant PMD-size
+ * ARCH_SUBSECTION_SHIFT can be set to a constant max size, or otherwise
+ * fallback to 2MB.
+ */
+#if defined(ARCH_SUBSECTION_SHIFT)
+#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
+#elif defined(PMD_SHIFT)
+#define SUBSECTION_SHIFT (PMD_SHIFT)
+#else
+/*
+ * Memory hotplug enabled platforms avoid this default because they
+ * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant, but
+ * this is kept as a backstop to allow compilation on
+ * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
+ */
+#define SUBSECTION_SHIFT 21
+#endif
+
+#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
+#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
+#define PAGE_SUBSECTION_MASK ((~(PAGES_PER_SUBSECTION-1)))
+
+#if SUBSECTION_SHIFT > SECTION_SIZE_BITS
+#error Subsection size exceeds section size
+#else
+#define SUBSECTIONS_PER_SECTION (1UL << (SECTION_SIZE_BITS - SUBSECTION_SHIFT))
+#endif
+
+struct mem_section_usage {
+	DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
+	/* See declaration of similar field in struct zone */
+	unsigned long pageblock_flags[0];
+};
+
 struct page;
 struct page_ext;
 struct mem_section {
@@ -1177,8 +1215,7 @@  struct mem_section {
 	 */
 	unsigned long section_mem_map;
 
-	/* See declaration of similar field in struct zone */
-	unsigned long *pageblock_flags;
+	struct mem_section_usage *usage;
 #ifdef CONFIG_PAGE_EXTENSION
 	/*
 	 * If SPARSEMEM, pgdat doesn't have page_ext pointer. We use
@@ -1209,6 +1246,11 @@  extern struct mem_section **mem_section;
 extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
 #endif
 
+static inline unsigned long *section_to_usemap(struct mem_section *ms)
+{
+	return ms->usage->pageblock_flags;
+}
+
 static inline struct mem_section *__nr_to_section(unsigned long nr)
 {
 #ifdef CONFIG_SPARSEMEM_EXTREME
@@ -1220,7 +1262,7 @@  static inline struct mem_section *__nr_to_section(unsigned long nr)
 	return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
 }
 extern int __section_nr(struct mem_section* ms);
-extern unsigned long usemap_size(void);
+extern size_t mem_section_usage_size(void);
 
 /*
  * We use the lower bits of the mem_map pointer to store
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 328878b6799d..a76fc6a6e9fe 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -165,9 +165,10 @@  void put_page_bootmem(struct page *page)
 #ifndef CONFIG_SPARSEMEM_VMEMMAP
 static void register_page_bootmem_info_section(unsigned long start_pfn)
 {
-	unsigned long *usemap, mapsize, section_nr, i;
+	unsigned long mapsize, section_nr, i;
 	struct mem_section *ms;
 	struct page *page, *memmap;
+	struct mem_section_usage *usage;
 
 	section_nr = pfn_to_section_nr(start_pfn);
 	ms = __nr_to_section(section_nr);
@@ -187,10 +188,10 @@  static void register_page_bootmem_info_section(unsigned long start_pfn)
 	for (i = 0; i < mapsize; i++, page++)
 		get_page_bootmem(section_nr, page, SECTION_INFO);
 
-	usemap = ms->pageblock_flags;
-	page = virt_to_page(usemap);
+	usage = ms->usage;
+	page = virt_to_page(usage);
 
-	mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;
+	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
 
 	for (i = 0; i < mapsize; i++, page++)
 		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
@@ -199,9 +200,10 @@  static void register_page_bootmem_info_section(unsigned long start_pfn)
 #else /* CONFIG_SPARSEMEM_VMEMMAP */
 static void register_page_bootmem_info_section(unsigned long start_pfn)
 {
-	unsigned long *usemap, mapsize, section_nr, i;
+	unsigned long mapsize, section_nr, i;
 	struct mem_section *ms;
 	struct page *page, *memmap;
+	struct mem_section_usage *usage;
 
 	section_nr = pfn_to_section_nr(start_pfn);
 	ms = __nr_to_section(section_nr);
@@ -210,10 +212,10 @@  static void register_page_bootmem_info_section(unsigned long start_pfn)
 
 	register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);
 
-	usemap = ms->pageblock_flags;
-	page = virt_to_page(usemap);
+	usage = ms->usage;
+	page = virt_to_page(usage);
 
-	mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;
+	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
 
 	for (i = 0; i < mapsize; i++, page++)
 		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1f99db76b1ff..61c2b54a5b61 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -403,7 +403,7 @@  static inline unsigned long *get_pageblock_bitmap(struct page *page,
 							unsigned long pfn)
 {
 #ifdef CONFIG_SPARSEMEM
-	return __pfn_to_section(pfn)->pageblock_flags;
+	return section_to_usemap(__pfn_to_section(pfn));
 #else
 	return page_zone(page)->pageblock_flags;
 #endif /* CONFIG_SPARSEMEM */
diff --git a/mm/sparse.c b/mm/sparse.c
index fd13166949b5..f87de7ad32c8 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -288,33 +288,31 @@  struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pn
 
 static void __meminit sparse_init_one_section(struct mem_section *ms,
 		unsigned long pnum, struct page *mem_map,
-		unsigned long *pageblock_bitmap)
+		struct mem_section_usage *usage)
 {
 	ms->section_mem_map &= ~SECTION_MAP_MASK;
 	ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum) |
 							SECTION_HAS_MEM_MAP;
- 	ms->pageblock_flags = pageblock_bitmap;
+	ms->usage = usage;
 }
 
-unsigned long usemap_size(void)
+static unsigned long usemap_size(void)
 {
 	return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);
 }
 
-#ifdef CONFIG_MEMORY_HOTPLUG
-static unsigned long *__kmalloc_section_usemap(void)
+size_t mem_section_usage_size(void)
 {
-	return kmalloc(usemap_size(), GFP_KERNEL);
+	return sizeof(struct mem_section_usage) + usemap_size();
 }
-#endif /* CONFIG_MEMORY_HOTPLUG */
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
-static unsigned long * __init
+static struct mem_section_usage * __init
 sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 					 unsigned long size)
 {
+	struct mem_section_usage *usage;
 	unsigned long goal, limit;
-	unsigned long *p;
 	int nid;
 	/*
 	 * A page may contain usemaps for other sections preventing the
@@ -330,15 +328,16 @@  sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 	limit = goal + (1UL << PA_SECTION_SHIFT);
 	nid = early_pfn_to_nid(goal >> PAGE_SHIFT);
 again:
-	p = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
-	if (!p && limit) {
+	usage = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
+	if (!usage && limit) {
 		limit = 0;
 		goto again;
 	}
-	return p;
+	return usage;
 }
 
-static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+static void __init check_usemap_section_nr(int nid,
+		struct mem_section_usage *usage)
 {
 	unsigned long usemap_snr, pgdat_snr;
 	static unsigned long old_usemap_snr;
@@ -352,7 +351,7 @@  static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
 		old_pgdat_snr = NR_MEM_SECTIONS;
 	}
 
-	usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
+	usemap_snr = pfn_to_section_nr(__pa(usage) >> PAGE_SHIFT);
 	pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
 	if (usemap_snr == pgdat_snr)
 		return;
@@ -380,14 +379,15 @@  static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
 		usemap_snr, pgdat_snr, nid);
 }
 #else
-static unsigned long * __init
+static struct mem_section_usage * __init
 sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 					 unsigned long size)
 {
 	return memblock_alloc_node(size, SMP_CACHE_BYTES, pgdat->node_id);
 }
 
-static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+static void __init check_usemap_section_nr(int nid,
+		struct mem_section_usage *usage)
 {
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
@@ -474,14 +474,13 @@  static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
 				   unsigned long pnum_end,
 				   unsigned long map_count)
 {
-	unsigned long pnum, usemap_longs, *usemap;
+	struct mem_section_usage *usage;
+	unsigned long pnum;
 	struct page *map;
 
-	usemap_longs = BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS);
-	usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
-							  usemap_size() *
-							  map_count);
-	if (!usemap) {
+	usage = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
+			mem_section_usage_size() * map_count);
+	if (!usage) {
 		pr_err("%s: node[%d] usemap allocation failed", __func__, nid);
 		goto failed;
 	}
@@ -497,9 +496,9 @@  static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
 			pnum_begin = pnum;
 			goto failed;
 		}
-		check_usemap_section_nr(nid, usemap);
-		sparse_init_one_section(__nr_to_section(pnum), pnum, map, usemap);
-		usemap += usemap_longs;
+		check_usemap_section_nr(nid, usage);
+		sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage);
+		usage = (void *) usage + mem_section_usage_size();
 	}
 	sparse_buffer_fini();
 	return;
@@ -701,9 +700,9 @@  int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
 				     struct vmem_altmap *altmap)
 {
 	unsigned long section_nr = pfn_to_section_nr(start_pfn);
+	struct mem_section_usage *usage;
 	struct mem_section *ms;
 	struct page *memmap;
-	unsigned long *usemap;
 	int ret;
 
 	/*
@@ -717,8 +716,8 @@  int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
 	memmap = kmalloc_section_memmap(section_nr, nid, altmap);
 	if (!memmap)
 		return -ENOMEM;
-	usemap = __kmalloc_section_usemap();
-	if (!usemap) {
+	usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
+	if (!usage) {
 		__kfree_section_memmap(memmap, altmap);
 		return -ENOMEM;
 	}
@@ -736,11 +735,11 @@  int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
 	page_init_poison(memmap, sizeof(struct page) * PAGES_PER_SECTION);
 
 	section_mark_present(ms);
-	sparse_init_one_section(ms, section_nr, memmap, usemap);
+	sparse_init_one_section(ms, section_nr, memmap, usage);
 
 out:
 	if (ret < 0) {
-		kfree(usemap);
+		kfree(usage);
 		__kfree_section_memmap(memmap, altmap);
 	}
 	return ret;
@@ -777,20 +776,20 @@  static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
 }
 #endif
 
-static void free_section_usemap(struct page *memmap, unsigned long *usemap,
-		struct vmem_altmap *altmap)
+static void free_section_usage(struct page *memmap,
+		struct mem_section_usage *usage, struct vmem_altmap *altmap)
 {
-	struct page *usemap_page;
+	struct page *usage_page;
 
-	if (!usemap)
+	if (!usage)
 		return;
 
-	usemap_page = virt_to_page(usemap);
+	usage_page = virt_to_page(usage);
 	/*
 	 * Check to see if allocation came from hot-plug-add
 	 */
-	if (PageSlab(usemap_page) || PageCompound(usemap_page)) {
-		kfree(usemap);
+	if (PageSlab(usage_page) || PageCompound(usage_page)) {
+		kfree(usage);
 		if (memmap)
 			__kfree_section_memmap(memmap, altmap);
 		return;
@@ -809,19 +808,19 @@  void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
 		unsigned long map_offset, struct vmem_altmap *altmap)
 {
 	struct page *memmap = NULL;
-	unsigned long *usemap = NULL;
+	struct mem_section_usage *usage = NULL;
 
 	if (ms->section_mem_map) {
-		usemap = ms->pageblock_flags;
+		usage = ms->usage;
 		memmap = sparse_decode_mem_map(ms->section_mem_map,
 						__section_nr(ms));
 		ms->section_mem_map = 0;
-		ms->pageblock_flags = NULL;
+		ms->usage = NULL;
 	}
 
 	clear_hwpoisoned_pages(memmap + map_offset,
 			PAGES_PER_SECTION - map_offset);
-	free_section_usemap(memmap, usemap, altmap);
+	free_section_usage(memmap, usage, altmap);
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 #endif /* CONFIG_MEMORY_HOTPLUG */