/*
 * Each physical page in the system has a struct page associated with
 * it to keep track of whatever it is we are using the page for at the
 * moment. Note that we have no way to track which tasks are using
 * a page, though if it is a pagecache page, rmap structures can tell us
 * who is mapping it.
 */
struct page {
	unsigned long flags;		/* Atomic flags, some possibly
					 * updated asynchronously */
	atomic_t _count;		/* Usage count, see below. */
	union {
		atomic_t _mapcount;	/* Count of ptes mapped in mms,
					 * to show when page is mapped
					 * & limit reverse map searches.
					 */
		struct {		/* SLUB */
			u16 inuse;
			u16 objects;
		};
	};
	union {
	    struct {
		unsigned long private;		/* Mapping-private opaque data:
					 	 * usually used for buffer_heads
						 * if PagePrivate set; used for
						 * swp_entry_t if PageSwapCache;
						 * indicates order in the buddy
						 * system if PG_buddy is set.
						 */
		struct address_space *mapping;	/* If low bit clear, points to
						 * inode address_space, or NULL.
						 * If page mapped as anonymous
						 * memory, low bit is set, and
						 * it points to anon_vma object:
						 * see PAGE_MAPPING_ANON below.
						 */
	    };
#if USE_SPLIT_PTLOCKS
	    spinlock_t ptl;
#endif
	    struct kmem_cache *slab;	/* SLUB: Pointer to slab */
	    struct page *first_page;	/* Compound tail pages */
	};
	union {
		pgoff_t index;		/* Our offset within mapping. */
		void *freelist;		/* SLUB: freelist req. slab lock */
	};
	struct list_head lru;		/* Pageout list, eg. active_list
					 * protected by zone->lru_lock !
					 */
	/*
	 * On machines where all RAM is mapped into kernel address space,
	 * we can simply calculate the virtual address. On machines with
	 * highmem some memory is mapped into kernel virtual memory
	 * dynamically, so we need a place to store that address.
	 * Note that this field could be 16 bits on x86 ... ;)
	 *
	 * Architectures with slow multiplication can define
	 * WANT_PAGE_VIRTUAL in asm/page.h
	 */
#if defined(WANT_PAGE_VIRTUAL)
	void *virtual;			/* Kernel virtual address (NULL if
					   not kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */
#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
	unsigned long debug_flags;	/* Use atomic bitops on this */
#endif

#ifdef CONFIG_KMEMCHECK
	/*
	 * kmemcheck wants to track the status of each byte in a page; this
	 * is a pointer to such a status block. NULL if not tracked.
	 */
	void *shadow;
#endif
};

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];

#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;
	int                     all_unreclaimable; /* All pages pinned */
#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;
#endif

	ZONE_PADDING(_pad1_)

	/* Fields commonly accessed by the page reclaim scanner */
	spinlock_t		lru_lock;
	struct zone_lru {
		struct list_head list;
	} lru[NR_LRU_LISTS];

	struct zone_reclaim_stat reclaim_stat;

	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;

	/*
	 * zone_start_pfn, spanned_pages and present_pages are all
	 * 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 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.
	 */
	unsigned long		spanned_pages;	/* total size, including holes */
	unsigned long		present_pages;	/* amount of memory (excluding holes) */

	/*
	 * rarely used fields:
	 */
	const char		*name;
} ____cacheline_internodealigned_in_smp;

struct page *alloc_pages(gfp_t gfp_mask, unsigned int order);

void *page_address(struct page *page);

unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);

unsigned long get_zeroed_page(gfp_t gfp_mask);

void __free_pages(struct page *page, unsigned int order);
void free_pages(unsigned long addr, unsigned int order);
void free_page(unsigned long addr);

/*
 * struct slab
 *
 * Manages the objs in a slab. Placed either at the beginning of mem allocated
 * for a slab, or allocated from an general cache.
 * Slabs are chained into three list: fully used, partial, fully free slabs.
 */
struct slab {
	union {
		struct {
			struct list_head list;     /* 满、部分或空链表 */
			unsigned long colouroff;   /* slab 着色偏移量 **/
			void *s_mem;		/* including colour offset */
			unsigned int inuse;	/* num of objs active in slab */
			kmem_bufctl_t free;
			unsigned short nodeid;
		};
		struct slab_rcu __slab_cover_slab_rcu;
	};
};

static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
{
	struct page *page;
	int nr_pages;
	int i;

#ifndef CONFIG_MMU
	/*
	 * Nommu uses slab's for process anonymous memory allocations, and thus
	 * requires __GFP_COMP to properly refcount higher order allocations
	 */
	flags |= __GFP_COMP;
#endif

	flags |= cachep->gfpflags;
	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
		flags |= __GFP_RECLAIMABLE;

	page = alloc_pages_exact_node(nodeid, flags | __GFP_NOTRACK, cachep->gfporder);
	if (!page)
		return NULL;

	nr_pages = (1 << cachep->gfporder);
	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
		add_zone_page_state(page_zone(page),
			NR_SLAB_RECLAIMABLE, nr_pages);
	else
		add_zone_page_state(page_zone(page),
			NR_SLAB_UNRECLAIMABLE, nr_pages);
	for (i = 0; i < nr_pages; i++)
		__SetPageSlab(page + i);

	if (kmemcheck_enabled && !(cachep->flags & SLAB_NOTRACK)) {
		kmemcheck_alloc_shadow(page, cachep->gfporder, flags, nodeid);

		if (cachep->ctor)
			kmemcheck_mark_uninitialized_pages(page, nr_pages);
		else
			kmemcheck_mark_unallocated_pages(page, nr_pages);
	}

	return page_address(page);
}

struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align,
			unsigned long flags,
			void (*ctor)(void *));

int kmem_cache_destory(struct kmem_cache *cachep);

void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags);

void kmem_cache_free(struct kmem_cache *cachep, void *objp);

void *kmap(struct page *page);

void kunmap(struct page *page);

void *kmap_atomic(struct page *page, enum km_type type);

void kunmap_atomic(void *kvaddr, enum km_type type);

// 定义和声明
DEFINE_PER_CPU(type, name);
DECLARE_PER_CPU(type, name);

// 操作接口
get_cpu_var(name);
put_cpu_var(name);

void *alloc_percpu(type);
void *__alloc_percpu(size_t size, size_t align );
void free_percpu(const void *);