text: /*
   * sparse memory mappings.
   */
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/mmzone.h>
  #include <linux/bootmem.h>
  #include <linux/compiler.h>
  #include <linux/highmem.h>
  #include <linux/export.h>
  #include <linux/spinlock.h>
  #include <linux/vmalloc.h>
  
  #include "internal.h"
  #include <asm/dma.h>
  #include <asm/pgalloc.h>
  #include <asm/pgtable.h>
  
  /*
   * Permanent SPARSEMEM data:
   *
   * 1) mem_section	- memory sections, mem_map's for valid memory
   */
  #ifdef CONFIG_SPARSEMEM_EXTREME
  struct mem_section *mem_section[NR_SECTION_ROOTS]
  	____cacheline_internodealigned_in_smp;
  #else
  struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
  	____cacheline_internodealigned_in_smp;
  #endif
  EXPORT_SYMBOL(mem_section);
  
  #ifdef NODE_NOT_IN_PAGE_FLAGS
  /*
   * If we did not store the node number in the page then we have to
   * do a lookup in the section_to_node_table in order to find which
   * node the page belongs to.
   */
  #if MAX_NUMNODES <= 256
  static u8 section_to_node_table[NR_MEM_SECTIONS] __cacheline_aligned;
  #else
  static u16 section_to_node_table[NR_MEM_SECTIONS] __cacheline_aligned;
  #endif
  
  int page_to_nid(const struct page *page)
  {
  	return section_to_node_table[page_to_section(page)];
  }
  EXPORT_SYMBOL(page_to_nid);
  
  static void set_section_nid(unsigned long section_nr, int nid)
  {
  	section_to_node_table[section_nr] = nid;
  }
  #else /* !NODE_NOT_IN_PAGE_FLAGS */
  static inline void set_section_nid(unsigned long section_nr, int nid)
  {
  }
  #endif
  
  #ifdef CONFIG_SPARSEMEM_EXTREME
  static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
  {
  	struct mem_section *section = NULL;
  	unsigned long array_size = SECTIONS_PER_ROOT *
  				   sizeof(struct mem_section);
  
  	if (slab_is_available()) {
  		if (node_state(nid, N_HIGH_MEMORY))
  			section = kzalloc_node(array_size, GFP_KERNEL, nid);
  		else
  			section = kzalloc(array_size, GFP_KERNEL);
  	} else {
  		section = memblock_virt_alloc_node(array_size, nid);
  	}
  
  	return section;
  }
  
  static int __meminit sparse_index_init(unsigned long section_nr, int nid)
  {
  	unsigned long root = SECTION_NR_TO_ROOT(section_nr);
  	struct mem_section *section;
  
  	if (mem_section[root])
  		return -EEXIST;
  
  	section = sparse_index_alloc(nid);
  	if (!section)
  		return -ENOMEM;
  
  	mem_section[root] = section;
  
  	return 0;
  }
  #else /* !SPARSEMEM_EXTREME */
  static inline int sparse_index_init(unsigned long section_nr, int nid)
  {
  	return 0;
  }
  #endif
  
  /*
   * Although written for the SPARSEMEM_EXTREME case, this happens
   * to also work for the flat array case because
   * NR_SECTION_ROOTS==NR_MEM_SECTIONS.
   */
  int __section_nr(struct mem_section* ms)
  {
  	unsigned long root_nr;
  	struct mem_section* root;
  
  	for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
  		root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
  		if (!root)
  			continue;
  
  		if ((ms >= root) && (ms < (root + SECTIONS_PER_ROOT)))
  		     break;
  	}
  
  	VM_BUG_ON(root_nr == NR_SECTION_ROOTS);
  
  	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
  }
  
  /*
   * During early boot, before section_mem_map is used for an actual
   * mem_map, we use section_mem_map to store the section's NUMA
   * node.  This keeps us from having to use another data structure.  The
   * node information is cleared just before we store the real mem_map.
   */
  static inline unsigned long sparse_encode_early_nid(int nid)
  {
  	return (nid << SECTION_NID_SHIFT);
  }
  
  static inline int sparse_early_nid(struct mem_section *section)
  {
  	return (section->section_mem_map >> SECTION_NID_SHIFT);
  }
  
  /* Validate the physical addressing limitations of the model */
  void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
  						unsigned long *end_pfn)
  {
  	unsigned long max_sparsemem_pfn = 1UL << (MAX_PHYSMEM_BITS-PAGE_SHIFT);
  
  	/*
  	 * Sanity checks - do not allow an architecture to pass
  	 * in larger pfns than the maximum scope of sparsemem:
  	 */
  	if (*start_pfn > max_sparsemem_pfn) {
  		mminit_dprintk(MMINIT_WARNING, "pfnvalidation",
  			"Start of range %lu -> %lu exceeds SPARSEMEM max %lu\n",
  			*start_pfn, *end_pfn, max_sparsemem_pfn);
  		WARN_ON_ONCE(1);
  		*start_pfn = max_sparsemem_pfn;
  		*end_pfn = max_sparsemem_pfn;
  	} else if (*end_pfn > max_sparsemem_pfn) {
  		mminit_dprintk(MMINIT_WARNING, "pfnvalidation",
  			"End of range %lu -> %lu exceeds SPARSEMEM max %lu\n",
  			*start_pfn, *end_pfn, max_sparsemem_pfn);
  		WARN_ON_ONCE(1);
  		*end_pfn = max_sparsemem_pfn;
  	}
  }
  
  /* Record a memory area against a node. */
  void __init memory_present(int nid, unsigned long start, unsigned long end)
  {
  	unsigned long pfn;
  
  	start &= PAGE_SECTION_MASK;
  	mminit_validate_memmodel_limits(&start, &end);
  	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
  		unsigned long section = pfn_to_section_nr(pfn);
  		struct mem_section *ms;
  
  		sparse_index_init(section, nid);
  		set_section_nid(section, nid);
  
  		ms = __nr_to_section(section);
  		if (!ms->section_mem_map)
  			ms->section_mem_map = sparse_encode_early_nid(nid) |
  							SECTION_MARKED_PRESENT;
  	}
  }
  
  /*
   * Only used by the i386 NUMA architecures, but relatively
   * generic code.
   */
  unsigned long __init node_memmap_size_bytes(int nid, unsigned long start_pfn,
  						     unsigned long end_pfn)
  {
  	unsigned long pfn;
  	unsigned long nr_pages = 0;
  
  	mminit_validate_memmodel_limits(&start_pfn, &end_pfn);
  	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
  		if (nid != early_pfn_to_nid(pfn))
  			continue;
  
  		if (pfn_present(pfn))
  			nr_pages += PAGES_PER_SECTION;
  	}
  
  	return nr_pages * sizeof(struct page);
  }
  
  /*
   * Subtle, we encode the real pfn into the mem_map such that
   * the identity pfn - section_mem_map will return the actual
   * physical page frame number.
   */
  static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
  {
  	return (unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
  }
  
  /*
   * Decode mem_map from the coded memmap
   */
  struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pnum)
  {
  	/* mask off the extra low bits of information */
  	coded_mem_map &= SECTION_MAP_MASK;
  	return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum);
  }
  
  static int __meminit sparse_init_one_section(struct mem_section *ms,
  		unsigned long pnum, struct page *mem_map,
  		unsigned long *pageblock_bitmap)
  {
  	if (!present_section(ms))
  		return -EINVAL;
  
  	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;
  
  	return 1;
  }
  
  unsigned long usemap_size(void)
  {
  	unsigned long size_bytes;
  	size_bytes = roundup(SECTION_BLOCKFLAGS_BITS, 8) / 8;
  	size_bytes = roundup(size_bytes, sizeof(unsigned long));
  	return size_bytes;
  }
  
  #ifdef CONFIG_MEMORY_HOTPLUG
  static unsigned long *__kmalloc_section_usemap(void)
  {
  	return kmalloc(usemap_size(), GFP_KERNEL);
  }
  #endif /* CONFIG_MEMORY_HOTPLUG */
  
  #ifdef CONFIG_MEMORY_HOTREMOVE
  static unsigned long * __init
  sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
  					 unsigned long size)
  {
  	unsigned long goal, limit;
  	unsigned long *p;
  	int nid;
  	/*
  	 * A page may contain usemaps for other sections preventing the
  	 * page being freed and making a section unremovable while
  	 * other sections referencing the usemap remain active. Similarly,
  	 * a pgdat can prevent a section being removed. If section A
  	 * contains a pgdat and section B contains the usemap, both
  	 * sections become inter-dependent. This allocates usemaps
  	 * from the same section as the pgdat where possible to avoid
  	 * this problem.
  	 */
  	goal = __pa(pgdat) & (PAGE_SECTION_MASK << PAGE_SHIFT);
  	limit = goal + (1UL << PA_SECTION_SHIFT);
  	nid = early_pfn_to_nid(goal >> PAGE_SHIFT);
  again:
  	p = memblock_virt_alloc_try_nid_nopanic(size,
  						SMP_CACHE_BYTES, goal, limit,
  						nid);
  	if (!p && limit) {
  		limit = 0;
  		goto again;
  	}
  	return p;
  }
  
  static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
  {
  	unsigned long usemap_snr, pgdat_snr;
  	static unsigned long old_usemap_snr = NR_MEM_SECTIONS;
  	static unsigned long old_pgdat_snr = NR_MEM_SECTIONS;
  	struct pglist_data *pgdat = NODE_DATA(nid);
  	int usemap_nid;
  
  	usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
  	pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
  	if (usemap_snr == pgdat_snr)
  		return;
  
  	if (old_usemap_snr == usemap_snr && old_pgdat_snr == pgdat_snr)
  		/* skip redundant message */
  		return;
  
  	old_usemap_snr = usemap_snr;
  	old_pgdat_snr = pgdat_snr;
  
  	usemap_nid = sparse_early_nid(__nr_to_section(usemap_snr));
  	if (usemap_nid != nid) {
  		printk(KERN_INFO
  		       "node %d must be removed before remove section %ld\n",
  		       nid, usemap_snr);
  		return;
  	}
  	/*
  	 * There is a circular dependency.
  	 * Some platforms allow un-removable section because they will just
  	 * gather other removable sections for dynamic partitioning.
  	 * Just notify un-removable section's number here.
  	 */
  	printk(KERN_INFO "Section %ld and %ld (node %d)", usemap_snr,
  	       pgdat_snr, nid);
  	printk(KERN_CONT
  	       " have a circular dependency on usemap and pgdat allocations\n");
  }
  #else
  static unsigned long * __init
  sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
  					 unsigned long size)
  {
  	return memblock_virt_alloc_node_nopanic(size, pgdat->node_id);
  }
  
  static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
  {
  }
  #endif /* CONFIG_MEMORY_HOTREMOVE */
  
  static void __init sparse_early_usemaps_alloc_node(void *data,
  				 unsigned long pnum_begin,
  				 unsigned long pnum_end,
  				 unsigned long usemap_count, int nodeid)
  {
  	void *usemap;
  	unsigned long pnum;
  	unsigned long **usemap_map = (unsigned long **)data;
  	int size = usemap_size();
  
  	usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nodeid),
  							  size * usemap_count);
  	if (!usemap) {
  		printk(KERN_WARNING "%s: allocation failed\n", __func__);
  		return;
  	}
  
  	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
  		if (!present_section_nr(pnum))
  			continue;
  		usemap_map[pnum] = usemap;
  		usemap += size;
  		check_usemap_section_nr(nodeid, usemap_map[pnum]);
  	}
  }
  
  #ifndef CONFIG_SPARSEMEM_VMEMMAP
  struct page __init *sparse_mem_map_populate(unsigned long pnum, int nid)
  {
  	struct page *map;
  	unsigned long size;
  
  	map = alloc_remap(nid, sizeof(struct page) * PAGES_PER_SECTION);
  	if (map)
  		return map;
  
  	size = PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION);
  	map = memblock_virt_alloc_try_nid(size,
  					  PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
  					  BOOTMEM_ALLOC_ACCESSIBLE, nid);
  	return map;
  }
  void __init sparse_mem_maps_populate_node(struct page **map_map,
  					  unsigned long pnum_begin,
  					  unsigned long pnum_end,
  					  unsigned long map_count, int nodeid)
  {
  	void *map;
  	unsigned long pnum;
  	unsigned long size = sizeof(struct page) * PAGES_PER_SECTION;
  
  	map = alloc_remap(nodeid, size * map_count);
  	if (map) {
  		for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
  			if (!present_section_nr(pnum))
  				continue;
  			map_map[pnum] = map;
  			map += size;
  		}
  		return;
  	}
  
  	size = PAGE_ALIGN(size);
  	map = memblock_virt_alloc_try_nid(size * map_count,
  					  PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
  					  BOOTMEM_ALLOC_ACCESSIBLE, nodeid);
  	if (map) {
  		for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
  			if (!present_section_nr(pnum))
  				continue;
  			map_map[pnum] = map;
  			map += size;
  		}
  		return;
  	}
  
  	/* fallback */
  	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
  		struct mem_section *ms;
  
  		if (!present_section_nr(pnum))
  			continue;
  		map_map[pnum] = sparse_mem_map_populate(pnum, nodeid);
  		if (map_map[pnum])
  			continue;
  		ms = __nr_to_section(pnum);
  		printk(KERN_ERR "%s: sparsemem memory map backing failed "
  			"some memory will not be available.\n", __func__);
  		ms->section_mem_map = 0;
  	}
  }
  #endif /* !CONFIG_SPARSEMEM_VMEMMAP */
  
  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
  static void __init sparse_early_mem_maps_alloc_node(void *data,
  				 unsigned long pnum_begin,
  				 unsigned long pnum_end,
  				 unsigned long map_count, int nodeid)
  {
  	struct page **map_map = (struct page **)data;
  	sparse_mem_maps_populate_node(map_map, pnum_begin, pnum_end,
  					 map_count, nodeid);
  }
  #else
  static struct page __init *sparse_early_mem_map_alloc(unsigned long pnum)
  {
  	struct page *map;
  	struct mem_section *ms = __nr_to_section(pnum);
  	int nid = sparse_early_nid(ms);
  
  	map = sparse_mem_map_populate(pnum, nid);
  	if (map)
  		return map;
  
  	printk(KERN_ERR "%s: sparsemem memory map backing failed "
  			"some memory will not be available.\n", __func__);
  	ms->section_mem_map = 0;
  	return NULL;
  }
  #endif
  
  void __weak __meminit vmemmap_populate_print_last(void)
  {
  }
  
  /**
   *  alloc_usemap_and_memmap - memory alloction for pageblock flags and vmemmap
   *  @map: usemap_map for pageblock flags or mmap_map for vmemmap
   */
  static void __init alloc_usemap_and_memmap(void (*alloc_func)
  					(void *, unsigned long, unsigned long,
  					unsigned long, int), void *data)
  {
  	unsigned long pnum;
  	unsigned long map_count;
  	int nodeid_begin = 0;
  	unsigned long pnum_begin = 0;
  
  	for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
  		struct mem_section *ms;
  
  		if (!present_section_nr(pnum))
  			continue;
  		ms = __nr_to_section(pnum);
  		nodeid_begin = sparse_early_nid(ms);
  		pnum_begin = pnum;
  		break;
  	}
  	map_count = 1;
  	for (pnum = pnum_begin + 1; pnum < NR_MEM_SECTIONS; pnum++) {
  		struct mem_section *ms;
  		int nodeid;
  
  		if (!present_section_nr(pnum))
  			continue;
  		ms = __nr_to_section(pnum);
  		nodeid = sparse_early_nid(ms);
  		if (nodeid == nodeid_begin) {
  			map_count++;
  			continue;
  		}
  		/* ok, we need to take cake of from pnum_begin to pnum - 1*/
  		alloc_func(data, pnum_begin, pnum,
  						map_count, nodeid_begin);
  		/* new start, update count etc*/
  		nodeid_begin = nodeid;
  		pnum_begin = pnum;
  		map_count = 1;
  	}
  	/* ok, last chunk */
  	alloc_func(data, pnum_begin, NR_MEM_SECTIONS,
  						map_count, nodeid_begin);
  }
  
  /*
   * Allocate the accumulated non-linear sections, allocate a mem_map
   * for each and record the physical to section mapping.
   */
  void __init sparse_init(void)
  {
  	unsigned long pnum;
  	struct page *map;
  	unsigned long *usemap;
  	unsigned long **usemap_map;
  	int size;
  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
  	int size2;
  	struct page **map_map;
  #endif
  
  	/* see include/linux/mmzone.h 'struct mem_section' definition */
  	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
  
  	/* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
  	set_pageblock_order();
  
  	/*
  	 * map is using big page (aka 2M in x86 64 bit)
  	 * usemap is less one page (aka 24 bytes)
  	 * so alloc 2M (with 2M align) and 24 bytes in turn will
  	 * make next 2M slip to one more 2M later.
  	 * then in big system, the memory will have a lot of holes...
  	 * here try to allocate 2M pages continuously.
  	 *
  	 * powerpc need to call sparse_init_one_section right after each
  	 * sparse_early_mem_map_alloc, so allocate usemap_map at first.
  	 */
  	size = sizeof(unsigned long *) * NR_MEM_SECTIONS;
  	usemap_map = memblock_virt_alloc(size, 0);
  	if (!usemap_map)
  		panic("can not allocate usemap_map\n");
  	alloc_usemap_and_memmap(sparse_early_usemaps_alloc_node,
  							(void *)usemap_map);
  
  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
  	size2 = sizeof(struct page *) * NR_MEM_SECTIONS;
  	map_map = memblock_virt_alloc(size2, 0);
  	if (!map_map)
  		panic("can not allocate map_map\n");
  	alloc_usemap_and_memmap(sparse_early_mem_maps_alloc_node,
  							(void *)map_map);
  #endif
  
  	for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
  		if (!present_section_nr(pnum))
  			continue;
  
  		usemap = usemap_map[pnum];
  		if (!usemap)
  			continue;
  
  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
  		map = map_map[pnum];
  #else
  		map = sparse_early_mem_map_alloc(pnum);
  #endif
  		if (!map)
  			continue;
  
  		sparse_init_one_section(__nr_to_section(pnum), pnum, map,
  								usemap);
  	}
  
  	vmemmap_populate_print_last();
  
  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
  	memblock_free_early(__pa(map_map), size2);
  #endif
  	memblock_free_early(__pa(usemap_map), size);
  }
  
  #ifdef CONFIG_MEMORY_HOTPLUG
  #ifdef CONFIG_SPARSEMEM_VMEMMAP
  static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid)
  {
  	/* This will make the necessary allocations eventually. */
  	return sparse_mem_map_populate(pnum, nid);
  }
  static void __kfree_section_memmap(struct page *memmap)
  {
  	unsigned long start = (unsigned long)memmap;
  	unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);
  
  	vmemmap_free(start, end);
  }
  #ifdef CONFIG_MEMORY_HOTREMOVE
  static void free_map_bootmem(struct page *memmap)
  {
  	unsigned long start = (unsigned long)memmap;
  	unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);
  
  	vmemmap_free(start, end);
  }
  #endif /* CONFIG_MEMORY_HOTREMOVE */
  #else
  static struct page *__kmalloc_section_memmap(void)
  {
  	struct page *page, *ret;
  	unsigned long memmap_size = sizeof(struct page) * PAGES_PER_SECTION;
  
  	page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
  	if (page)
  		goto got_map_page;
  
  	ret = vmalloc(memmap_size);
  	if (ret)
  		goto got_map_ptr;
  
  	return NULL;
  got_map_page:
  	ret = (struct page *)pfn_to_kaddr(page_to_pfn(page));
  got_map_ptr:
  
  	return ret;
  }
  
  static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid)
  {
  	return __kmalloc_section_memmap();
  }
  
  static void __kfree_section_memmap(struct page *memmap)
  {
  	if (is_vmalloc_addr(memmap))
  		vfree(memmap);
  	else
  		free_pages((unsigned long)memmap,
  			   get_order(sizeof(struct page) * PAGES_PER_SECTION));
  }
  
  #ifdef CONFIG_MEMORY_HOTREMOVE
  static void free_map_bootmem(struct page *memmap)
  {
  	unsigned long maps_section_nr, removing_section_nr, i;
  	unsigned long magic, nr_pages;
  	struct page *page = virt_to_page(memmap);
  
  	nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page))
  		>> PAGE_SHIFT;
  
  	for (i = 0; i < nr_pages; i++, page++) {
  		magic = (unsigned long) page->lru.next;
  
  		BUG_ON(magic == NODE_INFO);
  
  		maps_section_nr = pfn_to_section_nr(page_to_pfn(page));
  		removing_section_nr = page->private;
  
  		/*
  		 * When this function is called, the removing section is
  		 * logical offlined state. This means all pages are isolated
  		 * from page allocator. If removing section's memmap is placed
  		 * on the same section, it must not be freed.
  		 * If it is freed, page allocator may allocate it which will
  		 * be removed physically soon.
  		 */
  		if (maps_section_nr != removing_section_nr)
  			put_page_bootmem(page);
  	}
  }
  #endif /* CONFIG_MEMORY_HOTREMOVE */
  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
  
  /*
   * returns the number of sections whose mem_maps were properly
   * set.  If this is <=0, then that means that the passed-in
   * map was not consumed and must be freed.
   */
  int __meminit sparse_add_one_section(struct zone *zone, unsigned long start_pfn)
  {
  	unsigned long section_nr = pfn_to_section_nr(start_pfn);
  	struct pglist_data *pgdat = zone->zone_pgdat;
  	struct mem_section *ms;
  	struct page *memmap;
  	unsigned long *usemap;
  	unsigned long flags;
  	int ret;
  
  	/*
  	 * no locking for this, because it does its own
  	 * plus, it does a kmalloc
  	 */
  	ret = sparse_index_init(section_nr, pgdat->node_id);
  	if (ret < 0 && ret != -EEXIST)
  		return ret;
  	memmap = kmalloc_section_memmap(section_nr, pgdat->node_id);
  	if (!memmap)
  		return -ENOMEM;
  	usemap = __kmalloc_section_usemap();
  	if (!usemap) {
  		__kfree_section_memmap(memmap);
  		return -ENOMEM;
  	}
  
  	pgdat_resize_lock(pgdat, &flags);
  
  	ms = __pfn_to_section(start_pfn);
  	if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
  		ret = -EEXIST;
  		goto out;
  	}
  
  	memset(memmap, 0, sizeof(struct page) * PAGES_PER_SECTION);
  
  	ms->section_mem_map |= SECTION_MARKED_PRESENT;
  
  	ret = sparse_init_one_section(ms, section_nr, memmap, usemap);
  
  out:
  	pgdat_resize_unlock(pgdat, &flags);
  	if (ret <= 0) {
  		kfree(usemap);
  		__kfree_section_memmap(memmap);
  	}
  	return ret;
  }
  
  #ifdef CONFIG_MEMORY_HOTREMOVE
  #ifdef CONFIG_MEMORY_FAILURE
  static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
  {
  	int i;
  
  	if (!memmap)
  		return;
  
  	for (i = 0; i < PAGES_PER_SECTION; i++) {
  		if (PageHWPoison(&memmap[i])) {
  			atomic_long_sub(1, &num_poisoned_pages);
  			ClearPageHWPoison(&memmap[i]);
  		}
  	}
  }
  #else
  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 page *usemap_page;
  
  	if (!usemap)
  		return;
  
  	usemap_page = virt_to_page(usemap);
  	/*
  	 * Check to see if allocation came from hot-plug-add
  	 */
  	if (PageSlab(usemap_page) || PageCompound(usemap_page)) {
  		kfree(usemap);
  		if (memmap)
  			__kfree_section_memmap(memmap);
  		return;
  	}
  
  	/*
  	 * The usemap came from bootmem. This is packed with other usemaps
  	 * on the section which has pgdat at boot time. Just keep it as is now.
  	 */
  
  	if (memmap)
  		free_map_bootmem(memmap);
  }
  
  void sparse_remove_one_section(struct zone *zone, struct mem_section *ms)
  {
  	struct page *memmap = NULL;
  	unsigned long *usemap = NULL, flags;
  	struct pglist_data *pgdat = zone->zone_pgdat;
  
  	pgdat_resize_lock(pgdat, &flags);
  	if (ms->section_mem_map) {
  		usemap = ms->pageblock_flags;
  		memmap = sparse_decode_mem_map(ms->section_mem_map,
  						__section_nr(ms));
  		ms->section_mem_map = 0;
  		ms->pageblock_flags = NULL;
  	}
  	pgdat_resize_unlock(pgdat, &flags);
  
  	clear_hwpoisoned_pages(memmap, PAGES_PER_SECTION);
  	free_section_usemap(memmap, usemap);
  }
  #endif /* CONFIG_MEMORY_HOTREMOVE */
  #endif /* CONFIG_MEMORY_HOTPLUG */
  