#ifndef _LINUX_MMZONE_H
  #define _LINUX_MMZONE_H
  
  #ifndef __ASSEMBLY__
  #ifndef __GENERATING_BOUNDS_H
  
  #include <linux/spinlock.h>
  #include <linux/list.h>
  #include <linux/wait.h>
  #include <linux/bitops.h>
  #include <linux/cache.h>
  #include <linux/threads.h>
  #include <linux/numa.h>
  #include <linux/init.h>
  #include <linux/seqlock.h>
  #include <linux/nodemask.h>
  #include <linux/pageblock-flags.h>
  #include <linux/page-flags-layout.h>
  #include <linux/atomic.h>
  #include <asm/page.h>
  
  /* Free memory management - zoned buddy allocator.  */
  #ifndef CONFIG_FORCE_MAX_ZONEORDER
  #define MAX_ORDER 11
  #else
  #define MAX_ORDER CONFIG_FORCE_MAX_ZONEORDER
  #endif
  #define MAX_ORDER_NR_PAGES (1 << (MAX_ORDER - 1))
  
  /*
   * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed
   * costly to service.  That is between allocation orders which should
   * coalesce naturally under reasonable reclaim pressure and those which
   * will not.
   */
  #define PAGE_ALLOC_COSTLY_ORDER 3
  
  enum {
  	MIGRATE_UNMOVABLE,
  	MIGRATE_RECLAIMABLE,
  	MIGRATE_MOVABLE,
  	MIGRATE_PCPTYPES,	/* the number of types on the pcp lists */
  	MIGRATE_RESERVE = MIGRATE_PCPTYPES,
  #ifdef CONFIG_CMA
  	/*
  	 * MIGRATE_CMA migration type is designed to mimic the way
  	 * ZONE_MOVABLE works.  Only movable pages can be allocated
  	 * from MIGRATE_CMA pageblocks and page allocator never
  	 * implicitly change migration type of MIGRATE_CMA pageblock.
  	 *
  	 * The way to use it is to change migratetype of a range of
  	 * pageblocks to MIGRATE_CMA which can be done by
  	 * __free_pageblock_cma() function.  What is important though
  	 * is that a range of pageblocks must be aligned to
  	 * MAX_ORDER_NR_PAGES should biggest page be bigger then
  	 * a single pageblock.
  	 */
  	MIGRATE_CMA,
  #endif
  #ifdef CONFIG_MEMORY_ISOLATION
  	MIGRATE_ISOLATE,	/* can't allocate from here */
  #endif
  	MIGRATE_TYPES
  };
  
  #ifdef CONFIG_CMA
  #  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
  #else
  #  define is_migrate_cma(migratetype) false
  #endif
  
  #define for_each_migratetype_order(order, type) \
  	for (order = 0; order < MAX_ORDER; order++) \
  		for (type = 0; type < MIGRATE_TYPES; type++)
  
  extern int page_group_by_mobility_disabled;
  
  #define NR_MIGRATETYPE_BITS (PB_migrate_end - PB_migrate + 1)
  #define MIGRATETYPE_MASK ((1UL << NR_MIGRATETYPE_BITS) - 1)
  
  static inline int get_pageblock_migratetype(struct page *page)
  {
  	BUILD_BUG_ON(PB_migrate_end - PB_migrate != 2);
  	return get_pageblock_flags_mask(page, PB_migrate_end, MIGRATETYPE_MASK);
  }
  
  struct free_area {
  	struct list_head	free_list[MIGRATE_TYPES];
  	unsigned long		nr_free;
  };
  
  struct pglist_data;
  
  /*
   * zone->lock and zone->lru_lock are two of the hottest locks in the kernel.
   * So add a wild amount of padding here to ensure that they fall into separate
   * cachelines.  There are very few zone structures in the machine, so space
   * consumption is not a concern here.
   */
  #if defined(CONFIG_SMP)
  struct zone_padding {
  	char x[0];
  } ____cacheline_internodealigned_in_smp;
  #define ZONE_PADDING(name)	struct zone_padding name;
  #else
  #define ZONE_PADDING(name)
  #endif
  
  enum zone_stat_item {
  	/* First 128 byte cacheline (assuming 64 bit words) */
  	NR_FREE_PAGES,
  	NR_ALLOC_BATCH,
  	NR_LRU_BASE,
  	NR_INACTIVE_ANON = NR_LRU_BASE, /* must match order of LRU_[IN]ACTIVE */
  	NR_ACTIVE_ANON,		/*  "     "     "   "       "         */
  	NR_INACTIVE_FILE,	/*  "     "     "   "       "         */
  	NR_ACTIVE_FILE,		/*  "     "     "   "       "         */
  	NR_UNEVICTABLE,		/*  "     "     "   "       "         */
  	NR_MLOCK,		/* mlock()ed pages found and moved off LRU */
  	NR_ANON_PAGES,	/* Mapped anonymous pages */
  	NR_FILE_MAPPED,	/* pagecache pages mapped into pagetables.
  			   only modified from process context */
  	NR_FILE_PAGES,
  	NR_FILE_DIRTY,
  	NR_WRITEBACK,
  	NR_SLAB_RECLAIMABLE,
  	NR_SLAB_UNRECLAIMABLE,
  	NR_PAGETABLE,		/* used for pagetables */
  	NR_KERNEL_STACK,
  	/* Second 128 byte cacheline */
  	NR_UNSTABLE_NFS,	/* NFS unstable pages */
  	NR_BOUNCE,
  	NR_VMSCAN_WRITE,
  	NR_VMSCAN_IMMEDIATE,	/* Prioritise for reclaim when writeback ends */
  	NR_WRITEBACK_TEMP,	/* Writeback using temporary buffers */
  	NR_ISOLATED_ANON,	/* Temporary isolated pages from anon lru */
  	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
  	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
  	NR_DIRTIED,		/* page dirtyings since bootup */
  	NR_WRITTEN,		/* page writings since bootup */
  #ifdef CONFIG_NUMA
  	NUMA_HIT,		/* allocated in intended node */
  	NUMA_MISS,		/* allocated in non intended node */
  	NUMA_FOREIGN,		/* was intended here, hit elsewhere */
  	NUMA_INTERLEAVE_HIT,	/* interleaver preferred this zone */
  	NUMA_LOCAL,		/* allocation from local node */
  	NUMA_OTHER,		/* allocation from other node */
  #endif
  	NR_ANON_TRANSPARENT_HUGEPAGES,
  	NR_FREE_CMA_PAGES,
  	NR_VM_ZONE_STAT_ITEMS };
  
  /*
   * We do arithmetic on the LRU lists in various places in the code,
   * so it is important to keep the active lists LRU_ACTIVE higher in
   * the array than the corresponding inactive lists, and to keep
   * the *_FILE lists LRU_FILE higher than the corresponding _ANON lists.
   *
   * This has to be kept in sync with the statistics in zone_stat_item
   * above and the descriptions in vmstat_text in mm/vmstat.c
   */
  #define LRU_BASE 0
  #define LRU_ACTIVE 1
  #define LRU_FILE 2
  
  enum lru_list {
  	LRU_INACTIVE_ANON = LRU_BASE,
  	LRU_ACTIVE_ANON = LRU_BASE + LRU_ACTIVE,
  	LRU_INACTIVE_FILE = LRU_BASE + LRU_FILE,
  	LRU_ACTIVE_FILE = LRU_BASE + LRU_FILE + LRU_ACTIVE,
  	LRU_UNEVICTABLE,
  	NR_LRU_LISTS
  };
  
  #define for_each_lru(lru) for (lru = 0; lru < NR_LRU_LISTS; lru++)
  
  #define for_each_evictable_lru(lru) for (lru = 0; lru <= LRU_ACTIVE_FILE; lru++)
  
  static inline int is_file_lru(enum lru_list lru)
  {
  	return (lru == LRU_INACTIVE_FILE || lru == LRU_ACTIVE_FILE);
  }
  
  static inline int is_active_lru(enum lru_list lru)
  {
  	return (lru == LRU_ACTIVE_ANON || lru == LRU_ACTIVE_FILE);
  }
  
  static inline int is_unevictable_lru(enum lru_list lru)
  {
  	return (lru == LRU_UNEVICTABLE);
  }
  
  struct zone_reclaim_stat {
  	/*
  	 * The pageout code in vmscan.c keeps track of how many of the
  	 * mem/swap backed and file backed pages are referenced.
  	 * The higher the rotated/scanned ratio, the more valuable
  	 * that cache is.
  	 *
  	 * The anon LRU stats live in [0], file LRU stats in [1]
  	 */
  	unsigned long		recent_rotated[2];
  	unsigned long		recent_scanned[2];
  };
  
  struct lruvec {
  	struct list_head lists[NR_LRU_LISTS];
  	struct zone_reclaim_stat reclaim_stat;
  #ifdef CONFIG_MEMCG
  	struct zone *zone;
  #endif
  };
  
  /* Mask used at gathering information at once (see memcontrol.c) */
  #define LRU_ALL_FILE (BIT(LRU_INACTIVE_FILE) | BIT(LRU_ACTIVE_FILE))
  #define LRU_ALL_ANON (BIT(LRU_INACTIVE_ANON) | BIT(LRU_ACTIVE_ANON))
  #define LRU_ALL	     ((1 << NR_LRU_LISTS) - 1)
  
  /* Isolate clean file */
  #define ISOLATE_CLEAN		((__force isolate_mode_t)0x1)
  /* Isolate unmapped file */
  #define ISOLATE_UNMAPPED	((__force isolate_mode_t)0x2)
  /* Isolate for asynchronous migration */
  #define ISOLATE_ASYNC_MIGRATE	((__force isolate_mode_t)0x4)
  /* Isolate unevictable pages */
  #define ISOLATE_UNEVICTABLE	((__force isolate_mode_t)0x8)
  
  /* LRU Isolation modes. */
  typedef unsigned __bitwise__ isolate_mode_t;
  
  enum zone_watermarks {
  	WMARK_MIN,
  	WMARK_LOW,
  	WMARK_HIGH,
  	NR_WMARK
  };
  
  #define min_wmark_pages(z) (z->watermark[WMARK_MIN])
  #define low_wmark_pages(z) (z->watermark[WMARK_LOW])
  #define high_wmark_pages(z) (z->watermark[WMARK_HIGH])
  
  struct per_cpu_pages {
  	int count;		/* number of pages in the list */
  	int high;		/* high watermark, emptying needed */
  	int batch;		/* chunk size for buddy add/remove */
  
  	/* Lists of pages, one per migrate type stored on the pcp-lists */
  	struct list_head lists[MIGRATE_PCPTYPES];
  };
  
  struct per_cpu_pageset {
  	struct per_cpu_pages pcp;
  #ifdef CONFIG_NUMA
  	s8 expire;
  #endif
  #ifdef CONFIG_SMP
  	s8 stat_threshold;
  	s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
  #endif
  };
  
  #endif /* !__GENERATING_BOUNDS.H */
  
  enum zone_type {
  #ifdef CONFIG_ZONE_DMA
  	/*
  	 * ZONE_DMA is used when there are devices that are not able
  	 * to do DMA to all of addressable memory (ZONE_NORMAL). Then we
  	 * carve out the portion of memory that is needed for these devices.
  	 * The range is arch specific.
  	 *
  	 * Some examples
  	 *
  	 * Architecture		Limit
  	 * ---------------------------
  	 * parisc, ia64, sparc	<4G
  	 * s390			<2G
  	 * arm			Various
  	 * alpha		Unlimited or 0-16MB.
  	 *
  	 * i386, x86_64 and multiple other arches
  	 * 			<16M.
  	 */
  	ZONE_DMA,
  #endif
  #ifdef CONFIG_ZONE_DMA32
  	/*
  	 * x86_64 needs two ZONE_DMAs because it supports devices that are
  	 * only able to do DMA to the lower 16M but also 32 bit devices that
  	 * can only do DMA areas below 4G.
  	 */
  	ZONE_DMA32,
  #endif
  	/*
  	 * Normal addressable memory is in ZONE_NORMAL. DMA operations can be
  	 * performed on pages in ZONE_NORMAL if the DMA devices support
  	 * transfers to all addressable memory.
  	 */
  	ZONE_NORMAL,
  #ifdef CONFIG_HIGHMEM
  	/*
  	 * A memory area that is only addressable by the kernel through
  	 * mapping portions into its own address space. This is for example
  	 * used by i386 to allow the kernel to address the memory beyond
  	 * 900MB. The kernel will set up special mappings (page
  	 * table entries on i386) for each page that the kernel needs to
  	 * access.
  	 */
  	ZONE_HIGHMEM,
  #endif
  	ZONE_MOVABLE,
  	__MAX_NR_ZONES
  };
  
  #ifndef __GENERATING_BOUNDS_H
  
  struct zone {
  	/* Fields commonly accessed by the page allocator */
  
  	/* zone watermarks, access with *_wmark_pages(zone) macros */
  	unsigned long watermark[NR_WMARK];
  
  	/*
  	 * When free pages are below this point, additional steps are taken
  	 * when reading the number of free pages to avoid per-cpu counter
  	 * drift allowing watermarks to be breached
  	 */
  	unsigned long percpu_drift_mark;
  
  	/*
  	 * We don't know if the memory that we're going to allocate will be freeable
  	 * or/and it will be released eventually, so to avoid totally wasting several
  	 * GB of ram we must reserve some of the lower zone memory (otherwise we risk
  	 * to run OOM on the lower zones despite there's tons of freeable ram
  	 * on the higher zones). This array is recalculated at runtime if the
  	 * sysctl_lowmem_reserve_ratio sysctl changes.
  	 */
  	unsigned long		lowmem_reserve[MAX_NR_ZONES];
  
  	/*
  	 * This is a per-zone reserve of pages that should not be
  	 * considered dirtyable memory.
  	 */
  	unsigned long		dirty_balance_reserve;
  
  #ifdef CONFIG_NUMA
  	int node;
  	/*
  	 * zone reclaim becomes active if more unmapped pages exist.
  	 */
  	unsigned long		min_unmapped_pages;
  	unsigned long		min_slab_pages;
  #endif
  	struct per_cpu_pageset __percpu *pageset;
  	/*
  	 * free areas of different sizes
  	 */
  	spinlock_t		lock;
  #if defined CONFIG_COMPACTION || defined CONFIG_CMA
  	/* Set to true when the PG_migrate_skip bits should be cleared */
  	bool			compact_blockskip_flush;
  
  	/* pfn where compaction free scanner should start */
  	unsigned long		compact_cached_free_pfn;
  	/* pfn where async and sync compaction migration scanner should start */
  	unsigned long		compact_cached_migrate_pfn[2];
  #endif
  #ifdef CONFIG_MEMORY_HOTPLUG
  	/* see spanned/present_pages for more description */
  	seqlock_t		span_seqlock;
  #endif
  	struct free_area	free_area[MAX_ORDER];
  
  #ifndef CONFIG_SPARSEMEM
  	/*
  	 * Flags for a pageblock_nr_pages block. See pageblock-flags.h.
  	 * In SPARSEMEM, this map is stored in struct mem_section
  	 */
  	unsigned long		*pageblock_flags;
  #endif /* CONFIG_SPARSEMEM */
  
  #ifdef CONFIG_COMPACTION
  	/*
  	 * On compaction failure, 1<<compact_defer_shift compactions
  	 * are skipped before trying again. The number attempted since
  	 * last failure is tracked with compact_considered.
  	 */
  	unsigned int		compact_considered;
  	unsigned int		compact_defer_shift;
  	int			compact_order_failed;
  #endif
  
  	ZONE_PADDING(_pad1_)
  
  	/* Fields commonly accessed by the page reclaim scanner */
  	spinlock_t		lru_lock;
  	struct lruvec		lruvec;
  
  	unsigned long		pages_scanned;	   /* since last reclaim */
  	unsigned long		flags;		   /* zone flags, see below */
  
  	/* Zone statistics */
  	atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS];
  
  	/*
  	 * The target ratio of ACTIVE_ANON to INACTIVE_ANON pages on
  	 * this zone's LRU.  Maintained by the pageout code.
  	 */
  	unsigned int inactive_ratio;
  
  
  	ZONE_PADDING(_pad2_)
  	/* Rarely used or read-mostly fields */
  
  	/*
  	 * wait_table		-- the array holding the hash table
  	 * wait_table_hash_nr_entries	-- the size of the hash table array
  	 * wait_table_bits	-- wait_table_size == (1 << wait_table_bits)
  	 *
  	 * The purpose of all these is to keep track of the people
  	 * waiting for a page to become available and make them
  	 * runnable again when possible. The trouble is that this
  	 * consumes a lot of space, especially when so few things
  	 * wait on pages at a given time. So instead of using
  	 * per-page waitqueues, we use a waitqueue hash table.
  	 *
  	 * The bucket discipline is to sleep on the same queue when
  	 * colliding and wake all in that wait queue when removing.
  	 * When something wakes, it must check to be sure its page is
  	 * truly available, a la thundering herd. The cost of a
  	 * collision is great, but given the expected load of the
  	 * table, they should be so rare as to be outweighed by the
  	 * benefits from the saved space.
  	 *
  	 * __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the
  	 * primary users of these fields, and in mm/page_alloc.c
  	 * free_area_init_core() performs the initialization of them.
  	 */
  	wait_queue_head_t	* wait_table;
  	unsigned long		wait_table_hash_nr_entries;
  	unsigned long		wait_table_bits;
  
  	/*
  	 * Discontig memory support fields.
  	 */
  	struct pglist_data	*zone_pgdat;
  	/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
  	unsigned long		zone_start_pfn;
  
  	/*
  	 * spanned_pages is the total pages spanned by the zone, including
  	 * holes, which is calculated as:
  	 * 	spanned_pages = zone_end_pfn - zone_start_pfn;
  	 *
  	 * present_pages is physical pages existing within the zone, which
  	 * is calculated as:
  	 *	present_pages = spanned_pages - absent_pages(pages in holes);
  	 *
  	 * managed_pages is present pages managed by the buddy system, which
  	 * is calculated as (reserved_pages includes pages allocated by the
  	 * bootmem allocator):
  	 *	managed_pages = present_pages - reserved_pages;
  	 *
  	 * So present_pages may be used by memory hotplug or memory power
  	 * management logic to figure out unmanaged pages by checking
  	 * (present_pages - managed_pages). And managed_pages should be used
  	 * by page allocator and vm scanner to calculate all kinds of watermarks
  	 * and thresholds.
  	 *
  	 * Locking rules:
  	 *
  	 * zone_start_pfn and spanned_pages are protected by span_seqlock.
  	 * It is a seqlock because it has to be read outside of zone->lock,
  	 * and it is done in the main allocator path.  But, it is written
  	 * quite infrequently.
  	 *
  	 * The span_seq lock is declared along with zone->lock because it is
  	 * frequently read in proximity to zone->lock.  It's good to
  	 * give them a chance of being in the same cacheline.
  	 *
  	 * Write access to present_pages at runtime should be protected by
  	 * lock_memory_hotplug()/unlock_memory_hotplug().  Any reader who can't
  	 * tolerant drift of present_pages should hold memory hotplug lock to
  	 * get a stable value.
  	 *
  	 * Read access to managed_pages should be safe because it's unsigned
  	 * long. Write access to zone->managed_pages and totalram_pages are
  	 * protected by managed_page_count_lock at runtime. Idealy only
  	 * adjust_managed_page_count() should be used instead of directly
  	 * touching zone->managed_pages and totalram_pages.
  	 */
  	unsigned long		spanned_pages;
  	unsigned long		present_pages;
  	unsigned long		managed_pages;
  
  	/*
  	 * Number of MIGRATE_RESEVE page block. To maintain for just
  	 * optimization. Protected by zone->lock.
  	 */
  	int			nr_migrate_reserve_block;
  
  	/*
  	 * rarely used fields:
  	 */
  	const char		*name;
  } ____cacheline_internodealigned_in_smp;
  
  typedef enum {
  	ZONE_RECLAIM_LOCKED,		/* prevents concurrent reclaim */
  	ZONE_OOM_LOCKED,		/* zone is in OOM killer zonelist */
  	ZONE_CONGESTED,			/* zone has many dirty pages backed by
  					 * a congested BDI
  					 */
  	ZONE_TAIL_LRU_DIRTY,		/* reclaim scanning has recently found
  					 * many dirty file pages at the tail
  					 * of the LRU.
  					 */
  	ZONE_WRITEBACK,			/* reclaim scanning has recently found
  					 * many pages under writeback
  					 */
  } zone_flags_t;
  
  static inline void zone_set_flag(struct zone *zone, zone_flags_t flag)
  {
  	set_bit(flag, &zone->flags);
  }
  
  static inline int zone_test_and_set_flag(struct zone *zone, zone_flags_t flag)
  {
  	return test_and_set_bit(flag, &zone->flags);
  }
  
  static inline void zone_clear_flag(struct zone *zone, zone_flags_t flag)
  {
  	clear_bit(flag, &zone->flags);
  }
  
  static inline int zone_is_reclaim_congested(const struct zone *zone)
  {
  	return test_bit(ZONE_CONGESTED, &zone->flags);
  }
  
  static inline int zone_is_reclaim_dirty(const struct zone *zone)
  {
  	return test_bit(ZONE_TAIL_LRU_DIRTY, &zone->flags);
  }
  
  static inline int zone_is_reclaim_writeback(const struct zone *zone)
  {
  	return test_bit(ZONE_WRITEBACK, &zone->flags);
  }
  
  static inline int zone_is_reclaim_locked(const struct zone *zone)
  {
  	return test_bit(ZONE_RECLAIM_LOCKED, &zone->flags);
  }
  
  static inline int zone_is_oom_locked(const struct zone *zone)
  {
  	return test_bit(ZONE_OOM_LOCKED, &zone->flags);
  }
  
  static inline unsigned long zone_end_pfn(const struct zone *zone)
  {
  	return zone->zone_start_pfn + zone->spanned_pages;
  }
  
  static inline bool zone_spans_pfn(const struct zone *zone, unsigned long pfn)
  {
  	return zone->zone_start_pfn <= pfn && pfn < zone_end_pfn(zone);
  }
  
  static inline bool zone_is_initialized(struct zone *zone)
  {
  	return !!zone->wait_table;
  }
  
  static inline bool zone_is_empty(struct zone *zone)
  {
  	return zone->spanned_pages == 0;
  }
  
  /*
   * The "priority" of VM scanning is how much of the queues we will scan in one
   * go. A value of 12 for DEF_PRIORITY implies that we will scan 1/4096th of the
   * queues ("queue_length >> 12") during an aging round.
   */
  #define DEF_PRIORITY 12
  
  /* Maximum number of zones on a zonelist */
  #define MAX_ZONES_PER_ZONELIST (MAX_NUMNODES * MAX_NR_ZONES)
  
  #ifdef CONFIG_NUMA
  
  /*
   * The NUMA zonelists are doubled because we need zonelists that restrict the
   * allocations to a single node for __GFP_THISNODE.
   *
   * [0]	: Zonelist with fallback
   * [1]	: No fallback (__GFP_THISNODE)
   */
  #define MAX_ZONELISTS 2
  
  
  /*
   * We cache key information from each zonelist for smaller cache
   * footprint when scanning for free pages in get_page_from_freelist().
   *
   * 1) The BITMAP fullzones tracks which zones in a zonelist have come
   *    up short of free memory since the last time (last_fullzone_zap)
   *    we zero'd fullzones.
   * 2) The array z_to_n[] maps each zone in the zonelist to its node
   *    id, so that we can efficiently evaluate whether that node is
   *    set in the current tasks mems_allowed.
   *
   * Both fullzones and z_to_n[] are one-to-one with the zonelist,
   * indexed by a zones offset in the zonelist zones[] array.
   *
   * The get_page_from_freelist() routine does two scans.  During the
   * first scan, we skip zones whose corresponding bit in 'fullzones'
   * is set or whose corresponding node in current->mems_allowed (which
   * comes from cpusets) is not set.  During the second scan, we bypass
   * this zonelist_cache, to ensure we look methodically at each zone.
   *
   * Once per second, we zero out (zap) fullzones, forcing us to
   * reconsider nodes that might have regained more free memory.
   * The field last_full_zap is the time we last zapped fullzones.
   *
   * This mechanism reduces the amount of time we waste repeatedly
   * reexaming zones for free memory when they just came up low on
   * memory momentarilly ago.
   *
   * The zonelist_cache struct members logically belong in struct
   * zonelist.  However, the mempolicy zonelists constructed for
   * MPOL_BIND are intentionally variable length (and usually much
   * shorter).  A general purpose mechanism for handling structs with
   * multiple variable length members is more mechanism than we want
   * here.  We resort to some special case hackery instead.
   *
   * The MPOL_BIND zonelists don't need this zonelist_cache (in good
   * part because they are shorter), so we put the fixed length stuff
   * at the front of the zonelist struct, ending in a variable length
   * zones[], as is needed by MPOL_BIND.
   *
   * Then we put the optional zonelist cache on the end of the zonelist
   * struct.  This optional stuff is found by a 'zlcache_ptr' pointer in
   * the fixed length portion at the front of the struct.  This pointer
   * both enables us to find the zonelist cache, and in the case of
   * MPOL_BIND zonelists, (which will just set the zlcache_ptr to NULL)
   * to know that the zonelist cache is not there.
   *
   * The end result is that struct zonelists come in two flavors:
   *  1) The full, fixed length version, shown below, and
   *  2) The custom zonelists for MPOL_BIND.
   * The custom MPOL_BIND zonelists have a NULL zlcache_ptr and no zlcache.
   *
   * Even though there may be multiple CPU cores on a node modifying
   * fullzones or last_full_zap in the same zonelist_cache at the same
   * time, we don't lock it.  This is just hint data - if it is wrong now
   * and then, the allocator will still function, perhaps a bit slower.
   */
  
  
  struct zonelist_cache {
  	unsigned short z_to_n[MAX_ZONES_PER_ZONELIST];		/* zone->nid */
  	DECLARE_BITMAP(fullzones, MAX_ZONES_PER_ZONELIST);	/* zone full? */
  	unsigned long last_full_zap;		/* when last zap'd (jiffies) */
  };
  #else
  #define MAX_ZONELISTS 1
  struct zonelist_cache;
  #endif
  
  /*
   * This struct contains information about a zone in a zonelist. It is stored
   * here to avoid dereferences into large structures and lookups of tables
   */
  struct zoneref {
  	struct zone *zone;	/* Pointer to actual zone */
  	int zone_idx;		/* zone_idx(zoneref->zone) */
  };
  
  /*
   * One allocation request operates on a zonelist. A zonelist
   * is a list of zones, the first one is the 'goal' of the
   * allocation, the other zones are fallback zones, in decreasing
   * priority.
   *
   * If zlcache_ptr is not NULL, then it is just the address of zlcache,
   * as explained above.  If zlcache_ptr is NULL, there is no zlcache.
   * *
   * To speed the reading of the zonelist, the zonerefs contain the zone index
   * of the entry being read. Helper functions to access information given
   * a struct zoneref are
   *
   * zonelist_zone()	- Return the struct zone * for an entry in _zonerefs
   * zonelist_zone_idx()	- Return the index of the zone for an entry
   * zonelist_node_idx()	- Return the index of the node for an entry
   */
  struct zonelist {
  	struct zonelist_cache *zlcache_ptr;		     // NULL or &zlcache
  	struct zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
  #ifdef CONFIG_NUMA
  	struct zonelist_cache zlcache;			     // optional ...
  #endif
  };
  
  #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
  struct node_active_region {
  	unsigned long start_pfn;
  	unsigned long end_pfn;
  	int nid;
  };
  #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
  
  #ifndef CONFIG_DISCONTIGMEM
  /* The array of struct pages - for discontigmem use pgdat->lmem_map */
  extern struct page *mem_map;
  #endif
  
  /*
   * The pg_data_t structure is used in machines with CONFIG_DISCONTIGMEM
   * (mostly NUMA machines?) to denote a higher-level memory zone than the
   * zone denotes.
   *
   * On NUMA machines, each NUMA node would have a pg_data_t to describe
   * it's memory layout.
   *
   * Memory statistics and page replacement data structures are maintained on a
   * per-zone basis.
   */
  struct bootmem_data;
  typedef struct pglist_data {
  	struct zone node_zones[MAX_NR_ZONES];
  	struct zonelist node_zonelists[MAX_ZONELISTS];
  	int nr_zones;
  #ifdef CONFIG_FLAT_NODE_MEM_MAP	/* means !SPARSEMEM */
  	struct page *node_mem_map;
  #ifdef CONFIG_MEMCG
  	struct page_cgroup *node_page_cgroup;
  #endif
  #endif
  #ifndef CONFIG_NO_BOOTMEM
  	struct bootmem_data *bdata;
  #endif
  #ifdef CONFIG_MEMORY_HOTPLUG
  	/*
  	 * Must be held any time you expect node_start_pfn, node_present_pages
  	 * or node_spanned_pages stay constant.  Holding this will also
  	 * guarantee that any pfn_valid() stays that way.
  	 *
  	 * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
  	 * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG.
  	 *
  	 * Nests above zone->lock and zone->span_seqlock
  	 */
  	spinlock_t node_size_lock;
  #endif
  	unsigned long node_start_pfn;
  	unsigned long node_present_pages; /* total number of physical pages */
  	unsigned long node_spanned_pages; /* total size of physical page
  					     range, including holes */
  	int node_id;
  	nodemask_t reclaim_nodes;	/* Nodes allowed to reclaim from */
  	wait_queue_head_t kswapd_wait;
  	wait_queue_head_t pfmemalloc_wait;
  	struct task_struct *kswapd;	/* Protected by lock_memory_hotplug() */
  	int kswapd_max_order;
  	enum zone_type classzone_idx;
  #ifdef CONFIG_NUMA_BALANCING
  	/* Lock serializing the migrate rate limiting window */
  	spinlock_t numabalancing_migrate_lock;
  
  	/* Rate limiting time interval */
  	unsigned long numabalancing_migrate_next_window;
  
  	/* Number of pages migrated during the rate limiting time interval */
  	unsigned long numabalancing_migrate_nr_pages;
  #endif
  } pg_data_t;
  
  #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
  #define node_spanned_pages(nid)	(NODE_DATA(nid)->node_spanned_pages)
  #ifdef CONFIG_FLAT_NODE_MEM_MAP
  #define pgdat_page_nr(pgdat, pagenr)	((pgdat)->node_mem_map + (pagenr))
  #else
  #define pgdat_page_nr(pgdat, pagenr)	pfn_to_page((pgdat)->node_start_pfn + (pagenr))
  #endif
  #define nid_page_nr(nid, pagenr) 	pgdat_page_nr(NODE_DATA(nid),(pagenr))
  
  #define node_start_pfn(nid)	(NODE_DATA(nid)->node_start_pfn)
  #define node_end_pfn(nid) pgdat_end_pfn(NODE_DATA(nid))
  
  static inline unsigned long pgdat_end_pfn(pg_data_t *pgdat)
  {
  	return pgdat->node_start_pfn + pgdat->node_spanned_pages;
  }
  
  static inline bool pgdat_is_empty(pg_data_t *pgdat)
  {
  	return !pgdat->node_start_pfn && !pgdat->node_spanned_pages;
  }
  
  #include <linux/memory_hotplug.h>
  
  extern struct mutex zonelists_mutex;
  void build_all_zonelists(pg_data_t *pgdat, struct zone *zone);
  void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx);
  bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
  		int classzone_idx, int alloc_flags);
  bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
  		int classzone_idx, int alloc_flags);
  enum memmap_context {
  	MEMMAP_EARLY,
  	MEMMAP_HOTPLUG,
  };
  extern int init_currently_empty_zone(struct zone *zone, unsigned long start_pfn,
  				     unsigned long size,
  				     enum memmap_context context);
  
  extern void lruvec_init(struct lruvec *lruvec);
  
  static inline struct zone *lruvec_zone(struct lruvec *lruvec)
  {
  #ifdef CONFIG_MEMCG
  	return lruvec->zone;
  #else
  	return container_of(lruvec, struct zone, lruvec);
  #endif
  }
  
  #ifdef CONFIG_HAVE_MEMORY_PRESENT
  void memory_present(int nid, unsigned long start, unsigned long end);
  #else
  static inline void memory_present(int nid, unsigned long start, unsigned long end) {}
  #endif
  
  #ifdef CONFIG_HAVE_MEMORYLESS_NODES
  int local_memory_node(int node_id);
  #else
  static inline int local_memory_node(int node_id) { return node_id; };
  #endif
  
  #ifdef CONFIG_NEED_NODE_MEMMAP_SIZE
  unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long);
  #endif
  
  /*
   * zone_idx() returns 0 for the ZONE_DMA zone, 1 for the ZONE_NORMAL zone, etc.
   */
  #define zone_idx(zone)		((zone) - (zone)->zone_pgdat->node_zones)
  
  static inline int populated_zone(struct zone *zone)
  {
  	return (!!zone->present_pages);
  }
  
  extern int movable_zone;
  
  static inline int zone_movable_is_highmem(void)
  {
  #if defined(CONFIG_HIGHMEM) && defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
  	return movable_zone == ZONE_HIGHMEM;
  #else
  	return 0;
  #endif
  }
  
  static inline int is_highmem_idx(enum zone_type idx)
  {
  #ifdef CONFIG_HIGHMEM
  	return (idx == ZONE_HIGHMEM ||
  		(idx == ZONE_MOVABLE && zone_movable_is_highmem()));
  #else
  	return 0;
  #endif
  }
  
  /**
   * is_highmem - helper function to quickly check if a struct zone is a 
   *              highmem zone or not.  This is an attempt to keep references
   *              to ZONE_{DMA/NORMAL/HIGHMEM/etc} in general code to a minimum.
   * @zone - pointer to struct zone variable
   */
  static inline int is_highmem(struct zone *zone)
  {
  #ifdef CONFIG_HIGHMEM
  	int zone_off = (char *)zone - (char *)zone->zone_pgdat->node_zones;
  	return zone_off == ZONE_HIGHMEM * sizeof(*zone) ||
  	       (zone_off == ZONE_MOVABLE * sizeof(*zone) &&
  		zone_movable_is_highmem());
  #else
  	return 0;
  #endif
  }
  
  /* These two functions are used to setup the per zone pages min values */
  struct ctl_table;
  int min_free_kbytes_sysctl_handler(struct ctl_table *, int,
  					void __user *, size_t *, loff_t *);
  extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1];
  int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int,
  					void __user *, size_t *, loff_t *);
  int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
  					void __user *, size_t *, loff_t *);
  int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
  			void __user *, size_t *, loff_t *);
  int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
  			void __user *, size_t *, loff_t *);
  
  extern int numa_zonelist_order_handler(struct ctl_table *, int,
  			void __user *, size_t *, loff_t *);
  extern char numa_zonelist_order[];
  #define NUMA_ZONELIST_ORDER_LEN 16	/* string buffer size */
  
  #ifndef CONFIG_NEED_MULTIPLE_NODES
  
  extern struct pglist_data contig_page_data;
  #define NODE_DATA(nid)		(&contig_page_data)
  #define NODE_MEM_MAP(nid)	mem_map
  
  #else /* CONFIG_NEED_MULTIPLE_NODES */
  
  #include <asm/mmzone.h>
  
  #endif /* !CONFIG_NEED_MULTIPLE_NODES */
  
  extern struct pglist_data *first_online_pgdat(void);
  extern struct pglist_data *next_online_pgdat(struct pglist_data *pgdat);
  extern struct zone *next_zone(struct zone *zone);
  
  /**
   * for_each_online_pgdat - helper macro to iterate over all online nodes
   * @pgdat - pointer to a pg_data_t variable
   */
  #define for_each_online_pgdat(pgdat)			\
  	for (pgdat = first_online_pgdat();		\
  	     pgdat;					\
  	     pgdat = next_online_pgdat(pgdat))
  /**
   * for_each_zone - helper macro to iterate over all memory zones
   * @zone - pointer to struct zone variable
   *
   * The user only needs to declare the zone variable, for_each_zone
   * fills it in.
   */
  #define for_each_zone(zone)			        \
  	for (zone = (first_online_pgdat())->node_zones; \
  	     zone;					\
  	     zone = next_zone(zone))
  
  #define for_each_populated_zone(zone)		        \
  	for (zone = (first_online_pgdat())->node_zones; \
  	     zone;					\
  	     zone = next_zone(zone))			\
  		if (!populated_zone(zone))		\
  			; /* do nothing */		\
  		else
  
  static inline struct zone *zonelist_zone(struct zoneref *zoneref)
  {
  	return zoneref->zone;
  }
  
  static inline int zonelist_zone_idx(struct zoneref *zoneref)
  {
  	return zoneref->zone_idx;
  }
  
  static inline int zonelist_node_idx(struct zoneref *zoneref)
  {
  #ifdef CONFIG_NUMA
  	/* zone_to_nid not available in this context */
  	return zoneref->zone->node;
  #else
  	return 0;
  #endif /* CONFIG_NUMA */
  }
  
  /**
   * next_zones_zonelist - Returns the next zone at or below highest_zoneidx within the allowed nodemask using a cursor within a zonelist as a starting point
   * @z - The cursor used as a starting point for the search
   * @highest_zoneidx - The zone index of the highest zone to return
   * @nodes - An optional nodemask to filter the zonelist with
   * @zone - The first suitable zone found is returned via this parameter
   *
   * This function returns the next zone at or below a given zone index that is
   * within the allowed nodemask using a cursor as the starting point for the
   * search. The zoneref returned is a cursor that represents the current zone
   * being examined. It should be advanced by one before calling
   * next_zones_zonelist again.
   */
  struct zoneref *next_zones_zonelist(struct zoneref *z,
  					enum zone_type highest_zoneidx,
  					nodemask_t *nodes,
  					struct zone **zone);
  
  /**
   * first_zones_zonelist - Returns the first zone at or below highest_zoneidx within the allowed nodemask in a zonelist
   * @zonelist - The zonelist to search for a suitable zone
   * @highest_zoneidx - The zone index of the highest zone to return
   * @nodes - An optional nodemask to filter the zonelist with
   * @zone - The first suitable zone found is returned via this parameter
   *
   * This function returns the first zone at or below a given zone index that is
   * within the allowed nodemask. The zoneref returned is a cursor that can be
   * used to iterate the zonelist with next_zones_zonelist by advancing it by
   * one before calling.
   */
  static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
  					enum zone_type highest_zoneidx,
  					nodemask_t *nodes,
  					struct zone **zone)
  {
  	return next_zones_zonelist(zonelist->_zonerefs, highest_zoneidx, nodes,
  								zone);
  }
  
  /**
   * for_each_zone_zonelist_nodemask - helper macro to iterate over valid zones in a zonelist at or below a given zone index and within a nodemask
   * @zone - The current zone in the iterator
   * @z - The current pointer within zonelist->zones being iterated
   * @zlist - The zonelist being iterated
   * @highidx - The zone index of the highest zone to return
   * @nodemask - Nodemask allowed by the allocator
   *
   * This iterator iterates though all zones at or below a given zone index and
   * within a given nodemask
   */
  #define for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, nodemask) \
  	for (z = first_zones_zonelist(zlist, highidx, nodemask, &zone);	\
  		zone;							\
  		z = next_zones_zonelist(++z, highidx, nodemask, &zone))	\
  
  /**
   * for_each_zone_zonelist - helper macro to iterate over valid zones in a zonelist at or below a given zone index
   * @zone - The current zone in the iterator
   * @z - The current pointer within zonelist->zones being iterated
   * @zlist - The zonelist being iterated
   * @highidx - The zone index of the highest zone to return
   *
   * This iterator iterates though all zones at or below a given zone index.
   */
  #define for_each_zone_zonelist(zone, z, zlist, highidx) \
  	for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, NULL)
  
  #ifdef CONFIG_SPARSEMEM
  #include <asm/sparsemem.h>
  #endif
  
  #if !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) && \
  	!defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
  static inline unsigned long early_pfn_to_nid(unsigned long pfn)
  {
  	return 0;
  }
  #endif
  
  #ifdef CONFIG_FLATMEM
  #define pfn_to_nid(pfn)		(0)
  #endif
  
  #ifdef CONFIG_SPARSEMEM
  
  /*
   * SECTION_SHIFT    		#bits space required to store a section #
   *
   * PA_SECTION_SHIFT		physical address to/from section number
   * PFN_SECTION_SHIFT		pfn to/from section number
   */
  #define PA_SECTION_SHIFT	(SECTION_SIZE_BITS)
  #define PFN_SECTION_SHIFT	(SECTION_SIZE_BITS - PAGE_SHIFT)
  
  #define NR_MEM_SECTIONS		(1UL << SECTIONS_SHIFT)
  
  #define PAGES_PER_SECTION       (1UL << PFN_SECTION_SHIFT)
  #define PAGE_SECTION_MASK	(~(PAGES_PER_SECTION-1))
  
  #define SECTION_BLOCKFLAGS_BITS \
  	((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * NR_PAGEBLOCK_BITS)
  
  #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS
  #error Allocator MAX_ORDER exceeds SECTION_SIZE
  #endif
  
  #define pfn_to_section_nr(pfn) ((pfn) >> PFN_SECTION_SHIFT)
  #define section_nr_to_pfn(sec) ((sec) << PFN_SECTION_SHIFT)
  
  #define SECTION_ALIGN_UP(pfn)	(((pfn) + PAGES_PER_SECTION - 1) & PAGE_SECTION_MASK)
  #define SECTION_ALIGN_DOWN(pfn)	((pfn) & PAGE_SECTION_MASK)
  
  struct page;
  struct page_cgroup;
  struct mem_section {
  	/*
  	 * This is, logically, a pointer to an array of struct
  	 * pages.  However, it is stored with some other magic.
  	 * (see sparse.c::sparse_init_one_section())
  	 *
  	 * Additionally during early boot we encode node id of
  	 * the location of the section here to guide allocation.
  	 * (see sparse.c::memory_present())
  	 *
  	 * Making it a UL at least makes someone do a cast
  	 * before using it wrong.
  	 */
  	unsigned long section_mem_map;
  
  	/* See declaration of similar field in struct zone */
  	unsigned long *pageblock_flags;
  #ifdef CONFIG_MEMCG
  	/*
  	 * If !SPARSEMEM, pgdat doesn't have page_cgroup pointer. We use
  	 * section. (see memcontrol.h/page_cgroup.h about this.)
  	 */
  	struct page_cgroup *page_cgroup;
  	unsigned long pad;
  #endif
  	/*
  	 * WARNING: mem_section must be a power-of-2 in size for the
  	 * calculation and use of SECTION_ROOT_MASK to make sense.
  	 */
  };
  
  #ifdef CONFIG_SPARSEMEM_EXTREME
  #define SECTIONS_PER_ROOT       (PAGE_SIZE / sizeof (struct mem_section))
  #else
  #define SECTIONS_PER_ROOT	1
  #endif
  
  #define SECTION_NR_TO_ROOT(sec)	((sec) / SECTIONS_PER_ROOT)
  #define NR_SECTION_ROOTS	DIV_ROUND_UP(NR_MEM_SECTIONS, SECTIONS_PER_ROOT)
  #define SECTION_ROOT_MASK	(SECTIONS_PER_ROOT - 1)
  
  #ifdef CONFIG_SPARSEMEM_EXTREME
  extern struct mem_section *mem_section[NR_SECTION_ROOTS];
  #else
  extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
  #endif
  
  static inline struct mem_section *__nr_to_section(unsigned long nr)
  {
  	if (!mem_section[SECTION_NR_TO_ROOT(nr)])
  		return NULL;
  	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);
  
  /*
   * We use the lower bits of the mem_map pointer to store
   * a little bit of information.  There should be at least
   * 3 bits here due to 32-bit alignment.
   */
  #define	SECTION_MARKED_PRESENT	(1UL<<0)
  #define SECTION_HAS_MEM_MAP	(1UL<<1)
  #define SECTION_MAP_LAST_BIT	(1UL<<2)
  #define SECTION_MAP_MASK	(~(SECTION_MAP_LAST_BIT-1))
  #define SECTION_NID_SHIFT	2
  
  static inline struct page *__section_mem_map_addr(struct mem_section *section)
  {
  	unsigned long map = section->section_mem_map;
  	map &= SECTION_MAP_MASK;
  	return (struct page *)map;
  }
  
  static inline int present_section(struct mem_section *section)
  {
  	return (section && (section->section_mem_map & SECTION_MARKED_PRESENT));
  }
  
  static inline int present_section_nr(unsigned long nr)
  {
  	return present_section(__nr_to_section(nr));
  }
  
  static inline int valid_section(struct mem_section *section)
  {
  	return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP));
  }
  
  static inline int valid_section_nr(unsigned long nr)
  {
  	return valid_section(__nr_to_section(nr));
  }
  
  static inline struct mem_section *__pfn_to_section(unsigned long pfn)
  {
  	return __nr_to_section(pfn_to_section_nr(pfn));
  }
  
  #ifndef CONFIG_HAVE_ARCH_PFN_VALID
  static inline int pfn_valid(unsigned long pfn)
  {
  	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
  		return 0;
  	return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
  }
  #endif
  
  static inline int pfn_present(unsigned long pfn)
  {
  	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
  		return 0;
  	return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
  }
  
  /*
   * These are _only_ used during initialisation, therefore they
   * can use __initdata ...  They could have names to indicate
   * this restriction.
   */
  #ifdef CONFIG_NUMA
  #define pfn_to_nid(pfn)							\
  ({									\
  	unsigned long __pfn_to_nid_pfn = (pfn);				\
  	page_to_nid(pfn_to_page(__pfn_to_nid_pfn));			\
  })
  #else
  #define pfn_to_nid(pfn)		(0)
  #endif
  
  #define early_pfn_valid(pfn)	pfn_valid(pfn)
  void sparse_init(void);
  #else
  #define sparse_init()	do {} while (0)
  #define sparse_index_init(_sec, _nid)  do {} while (0)
  #endif /* CONFIG_SPARSEMEM */
  
  #ifdef CONFIG_NODES_SPAN_OTHER_NODES
  bool early_pfn_in_nid(unsigned long pfn, int nid);
  #else
  #define early_pfn_in_nid(pfn, nid)	(1)
  #endif
  
  #ifndef early_pfn_valid
  #define early_pfn_valid(pfn)	(1)
  #endif
  
  void memory_present(int nid, unsigned long start, unsigned long end);
  unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long);
  
  /*
   * If it is possible to have holes within a MAX_ORDER_NR_PAGES, then we
   * need to check pfn validility within that MAX_ORDER_NR_PAGES block.
   * pfn_valid_within() should be used in this case; we optimise this away
   * when we have no holes within a MAX_ORDER_NR_PAGES block.
   */
  #ifdef CONFIG_HOLES_IN_ZONE
  #define pfn_valid_within(pfn) pfn_valid(pfn)
  #else
  #define pfn_valid_within(pfn) (1)
  #endif
  
  #ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
  /*
   * pfn_valid() is meant to be able to tell if a given PFN has valid memmap
   * associated with it or not. In FLATMEM, it is expected that holes always
   * have valid memmap as long as there is valid PFNs either side of the hole.
   * In SPARSEMEM, it is assumed that a valid section has a memmap for the
   * entire section.
   *
   * However, an ARM, and maybe other embedded architectures in the future
   * free memmap backing holes to save memory on the assumption the memmap is
   * never used. The page_zone linkages are then broken even though pfn_valid()
   * returns true. A walker of the full memmap must then do this additional
   * check to ensure the memmap they are looking at is sane by making sure
   * the zone and PFN linkages are still valid. This is expensive, but walkers
   * of the full memmap are extremely rare.
   */
  int memmap_valid_within(unsigned long pfn,
  					struct page *page, struct zone *zone);
  #else
  static inline int memmap_valid_within(unsigned long pfn,
  					struct page *page, struct zone *zone)
  {
  	return 1;
  }
  #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
  
  #endif /* !__GENERATING_BOUNDS.H */
  #endif /* !__ASSEMBLY__ */
  #endif /* _LINUX_MMZONE_H */