tty: add kernel-doc for tty_driver

[linux-2.6-microblaze.git] / include / linux / mmzone.h

/* SPDX-License-Identifier: GPL-2.0 */
#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 <linux/mm_types.h>
#include <linux/page-flags.h>
#include <linux/local_lock.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 migratetype {
        MIGRATE_UNMOVABLE,
        MIGRATE_MOVABLE,
        MIGRATE_RECLAIMABLE,
        MIGRATE_PCPTYPES,       /* the number of types on the pcp lists */
        MIGRATE_HIGHATOMIC = 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 than
         * a single pageblock.
         */
        MIGRATE_CMA,
#endif
#ifdef CONFIG_MEMORY_ISOLATION
        MIGRATE_ISOLATE,        /* can't allocate from here */
#endif
        MIGRATE_TYPES
};

/* In mm/page_alloc.c; keep in sync also with show_migration_types() there */
extern const char * const migratetype_names[MIGRATE_TYPES];

#ifdef CONFIG_CMA
#  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
#  define is_migrate_cma_page(_page) (get_pageblock_migratetype(_page) == MIGRATE_CMA)
#else
#  define is_migrate_cma(migratetype) false
#  define is_migrate_cma_page(_page) false
#endif

static inline bool is_migrate_movable(int mt)
{
        return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
}

#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 MIGRATETYPE_MASK ((1UL << PB_migratetype_bits) - 1)

#define get_pageblock_migratetype(page)                                 \
        get_pfnblock_flags_mask(page, page_to_pfn(page), MIGRATETYPE_MASK)

struct free_area {
        struct list_head        free_list[MIGRATE_TYPES];
        unsigned long           nr_free;
};

static inline struct page *get_page_from_free_area(struct free_area *area,
                                            int migratetype)
{
        return list_first_entry_or_null(&area->free_list[migratetype],
                                        struct page, lru);
}

static inline bool free_area_empty(struct free_area *area, int migratetype)
{
        return list_empty(&area->free_list[migratetype]);
}

struct pglist_data;

/*
 * Add a wild amount of padding here to ensure data 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

#ifdef CONFIG_NUMA
enum numa_stat_item {
        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 */
        NR_VM_NUMA_EVENT_ITEMS
};
#else
#define NR_VM_NUMA_EVENT_ITEMS 0
#endif

enum zone_stat_item {
        /* First 128 byte cacheline (assuming 64 bit words) */
        NR_FREE_PAGES,
        NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
        NR_ZONE_INACTIVE_ANON = NR_ZONE_LRU_BASE,
        NR_ZONE_ACTIVE_ANON,
        NR_ZONE_INACTIVE_FILE,
        NR_ZONE_ACTIVE_FILE,
        NR_ZONE_UNEVICTABLE,
        NR_ZONE_WRITE_PENDING,  /* Count of dirty, writeback and unstable pages */
        NR_MLOCK,               /* mlock()ed pages found and moved off LRU */
        /* Second 128 byte cacheline */
        NR_BOUNCE,
#if IS_ENABLED(CONFIG_ZSMALLOC)
        NR_ZSPAGES,             /* allocated in zsmalloc */
#endif
        NR_FREE_CMA_PAGES,
        NR_VM_ZONE_STAT_ITEMS };

enum node_stat_item {
        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_SLAB_RECLAIMABLE_B,
        NR_SLAB_UNRECLAIMABLE_B,
        NR_ISOLATED_ANON,       /* Temporary isolated pages from anon lru */
        NR_ISOLATED_FILE,       /* Temporary isolated pages from file lru */
        WORKINGSET_NODES,
        WORKINGSET_REFAULT_BASE,
        WORKINGSET_REFAULT_ANON = WORKINGSET_REFAULT_BASE,
        WORKINGSET_REFAULT_FILE,
        WORKINGSET_ACTIVATE_BASE,
        WORKINGSET_ACTIVATE_ANON = WORKINGSET_ACTIVATE_BASE,
        WORKINGSET_ACTIVATE_FILE,
        WORKINGSET_RESTORE_BASE,
        WORKINGSET_RESTORE_ANON = WORKINGSET_RESTORE_BASE,
        WORKINGSET_RESTORE_FILE,
        WORKINGSET_NODERECLAIM,
        NR_ANON_MAPPED, /* 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_WRITEBACK_TEMP,      /* Writeback using temporary buffers */
        NR_SHMEM,               /* shmem pages (included tmpfs/GEM pages) */
        NR_SHMEM_THPS,
        NR_SHMEM_PMDMAPPED,
        NR_FILE_THPS,
        NR_FILE_PMDMAPPED,
        NR_ANON_THPS,
        NR_VMSCAN_WRITE,
        NR_VMSCAN_IMMEDIATE,    /* Prioritise for reclaim when writeback ends */
        NR_DIRTIED,             /* page dirtyings since bootup */
        NR_WRITTEN,             /* page writings since bootup */
        NR_THROTTLED_WRITTEN,   /* NR_WRITTEN while reclaim throttled */
        NR_KERNEL_MISC_RECLAIMABLE,     /* reclaimable non-slab kernel pages */
        NR_FOLL_PIN_ACQUIRED,   /* via: pin_user_page(), gup flag: FOLL_PIN */
        NR_FOLL_PIN_RELEASED,   /* pages returned via unpin_user_page() */
        NR_KERNEL_STACK_KB,     /* measured in KiB */
#if IS_ENABLED(CONFIG_SHADOW_CALL_STACK)
        NR_KERNEL_SCS_KB,       /* measured in KiB */
#endif
        NR_PAGETABLE,           /* used for pagetables */
#ifdef CONFIG_SWAP
        NR_SWAPCACHE,
#endif
        NR_VM_NODE_STAT_ITEMS
};

/*
 * Returns true if the item should be printed in THPs (/proc/vmstat
 * currently prints number of anon, file and shmem THPs. But the item
 * is charged in pages).
 */
static __always_inline bool vmstat_item_print_in_thp(enum node_stat_item item)
{
        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
                return false;

        return item == NR_ANON_THPS ||
               item == NR_FILE_THPS ||
               item == NR_SHMEM_THPS ||
               item == NR_SHMEM_PMDMAPPED ||
               item == NR_FILE_PMDMAPPED;
}

/*
 * Returns true if the value is measured in bytes (most vmstat values are
 * measured in pages). This defines the API part, the internal representation
 * might be different.
 */
static __always_inline bool vmstat_item_in_bytes(int idx)
{
        /*
         * Global and per-node slab counters track slab pages.
         * It's expected that changes are multiples of PAGE_SIZE.
         * Internally values are stored in pages.
         *
         * Per-memcg and per-lruvec counters track memory, consumed
         * by individual slab objects. These counters are actually
         * byte-precise.
         */
        return (idx == NR_SLAB_RECLAIMABLE_B ||
                idx == NR_SLAB_UNRECLAIMABLE_B);
}

/*
 * 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
};

enum vmscan_throttle_state {
        VMSCAN_THROTTLE_WRITEBACK,
        VMSCAN_THROTTLE_ISOLATED,
        VMSCAN_THROTTLE_NOPROGRESS,
        NR_VMSCAN_THROTTLE,
};

#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 bool is_file_lru(enum lru_list lru)
{
        return (lru == LRU_INACTIVE_FILE || lru == LRU_ACTIVE_FILE);
}

static inline bool is_active_lru(enum lru_list lru)
{
        return (lru == LRU_ACTIVE_ANON || lru == LRU_ACTIVE_FILE);
}

#define ANON_AND_FILE 2

enum lruvec_flags {
        LRUVEC_CONGESTED,               /* lruvec has many dirty pages
                                         * backed by a congested BDI
                                         */
};

struct lruvec {
        struct list_head                lists[NR_LRU_LISTS];
        /* per lruvec lru_lock for memcg */
        spinlock_t                      lru_lock;
        /*
         * These track the cost of reclaiming one LRU - file or anon -
         * over the other. As the observed cost of reclaiming one LRU
         * increases, the reclaim scan balance tips toward the other.
         */
        unsigned long                   anon_cost;
        unsigned long                   file_cost;
        /* Non-resident age, driven by LRU movement */
        atomic_long_t                   nonresident_age;
        /* Refaults at the time of last reclaim cycle */
        unsigned long                   refaults[ANON_AND_FILE];
        /* Various lruvec state flags (enum lruvec_flags) */
        unsigned long                   flags;
#ifdef CONFIG_MEMCG
        struct pglist_data *pgdat;
#endif
};

/* Isolate unmapped pages */
#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
};

/*
 * One per migratetype for each PAGE_ALLOC_COSTLY_ORDER plus one additional
 * for pageblock size for THP if configured.
 */
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define NR_PCP_THP 1
#else
#define NR_PCP_THP 0
#endif
#define NR_PCP_LISTS (MIGRATE_PCPTYPES * (PAGE_ALLOC_COSTLY_ORDER + 1 + NR_PCP_THP))

/*
 * Shift to encode migratetype and order in the same integer, with order
 * in the least significant bits.
 */
#define NR_PCP_ORDER_WIDTH 8
#define NR_PCP_ORDER_MASK ((1<<NR_PCP_ORDER_WIDTH) - 1)

#define min_wmark_pages(z) (z->_watermark[WMARK_MIN] + z->watermark_boost)
#define low_wmark_pages(z) (z->_watermark[WMARK_LOW] + z->watermark_boost)
#define high_wmark_pages(z) (z->_watermark[WMARK_HIGH] + z->watermark_boost)
#define wmark_pages(z, i) (z->_watermark[i] + z->watermark_boost)

/* Fields and list protected by pagesets local_lock in page_alloc.c */
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 */
        short free_factor;      /* batch scaling factor during free */
#ifdef CONFIG_NUMA
        short expire;           /* When 0, remote pagesets are drained */
#endif

        /* Lists of pages, one per migrate type stored on the pcp-lists */
        struct list_head lists[NR_PCP_LISTS];
};

struct per_cpu_zonestat {
#ifdef CONFIG_SMP
        s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
        s8 stat_threshold;
#endif
#ifdef CONFIG_NUMA
        /*
         * Low priority inaccurate counters that are only folded
         * on demand. Use a large type to avoid the overhead of
         * folding during refresh_cpu_vm_stats.
         */
        unsigned long vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
#endif
};

struct per_cpu_nodestat {
        s8 stat_threshold;
        s8 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
};

#endif /* !__GENERATING_BOUNDS.H */

enum zone_type {
        /*
         * ZONE_DMA and ZONE_DMA32 are used when there are peripherals not able
         * to DMA to all of the addressable memory (ZONE_NORMAL).
         * On architectures where this area covers the whole 32 bit address
         * space ZONE_DMA32 is used. ZONE_DMA is left for the ones with smaller
         * DMA addressing constraints. This distinction is important as a 32bit
         * DMA mask is assumed when ZONE_DMA32 is defined. Some 64-bit
         * platforms may need both zones as they support peripherals with
         * different DMA addressing limitations.
         */
#ifdef CONFIG_ZONE_DMA
        ZONE_DMA,
#endif
#ifdef CONFIG_ZONE_DMA32
        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 is similar to ZONE_NORMAL, except that it contains
         * movable pages with few exceptional cases described below. Main use
         * cases for ZONE_MOVABLE are to make memory offlining/unplug more
         * likely to succeed, and to locally limit unmovable allocations - e.g.,
         * to increase the number of THP/huge pages. Notable special cases are:
         *
         * 1. Pinned pages: (long-term) pinning of movable pages might
         *    essentially turn such pages unmovable. Therefore, we do not allow
         *    pinning long-term pages in ZONE_MOVABLE. When pages are pinned and
         *    faulted, they come from the right zone right away. However, it is
         *    still possible that address space already has pages in
         *    ZONE_MOVABLE at the time when pages are pinned (i.e. user has
         *    touches that memory before pinning). In such case we migrate them
         *    to a different zone. When migration fails - pinning fails.
         * 2. memblock allocations: kernelcore/movablecore setups might create
         *    situations where ZONE_MOVABLE contains unmovable allocations
         *    after boot. Memory offlining and allocations fail early.
         * 3. Memory holes: kernelcore/movablecore setups might create very rare
         *    situations where ZONE_MOVABLE contains memory holes after boot,
         *    for example, if we have sections that are only partially
         *    populated. Memory offlining and allocations fail early.
         * 4. PG_hwpoison pages: while poisoned pages can be skipped during
         *    memory offlining, such pages cannot be allocated.
         * 5. Unmovable PG_offline pages: in paravirtualized environments,
         *    hotplugged memory blocks might only partially be managed by the
         *    buddy (e.g., via XEN-balloon, Hyper-V balloon, virtio-mem). The
         *    parts not manged by the buddy are unmovable PG_offline pages. In
         *    some cases (virtio-mem), such pages can be skipped during
         *    memory offlining, however, cannot be moved/allocated. These
         *    techniques might use alloc_contig_range() to hide previously
         *    exposed pages from the buddy again (e.g., to implement some sort
         *    of memory unplug in virtio-mem).
         * 6. ZERO_PAGE(0), kernelcore/movablecore setups might create
         *    situations where ZERO_PAGE(0) which is allocated differently
         *    on different platforms may end up in a movable zone. ZERO_PAGE(0)
         *    cannot be migrated.
         * 7. Memory-hotplug: when using memmap_on_memory and onlining the
         *    memory to the MOVABLE zone, the vmemmap pages are also placed in
         *    such zone. Such pages cannot be really moved around as they are
         *    self-stored in the range, but they are treated as movable when
         *    the range they describe is about to be offlined.
         *
         * In general, no unmovable allocations that degrade memory offlining
         * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())
         * have to expect that migrating pages in ZONE_MOVABLE can fail (even
         * if has_unmovable_pages() states that there are no unmovable pages,
         * there can be false negatives).
         */
        ZONE_MOVABLE,
#ifdef CONFIG_ZONE_DEVICE
        ZONE_DEVICE,
#endif
        __MAX_NR_ZONES

};

#ifndef __GENERATING_BOUNDS_H

#define ASYNC_AND_SYNC 2

struct zone {
        /* Read-mostly fields */

        /* zone watermarks, access with *_wmark_pages(zone) macros */
        unsigned long _watermark[NR_WMARK];
        unsigned long watermark_boost;

        unsigned long nr_reserved_highatomic;

        /*
         * 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 being tons of freeable ram on the higher zones).  This array is
         * recalculated at runtime if the sysctl_lowmem_reserve_ratio sysctl
         * changes.
         */
        long lowmem_reserve[MAX_NR_ZONES];

#ifdef CONFIG_NUMA
        int node;
#endif
        struct pglist_data      *zone_pgdat;
        struct per_cpu_pages    __percpu *per_cpu_pageset;
        struct per_cpu_zonestat __percpu *per_cpu_zonestats;
        /*
         * the high and batch values are copied to individual pagesets for
         * faster access
         */
        int pageset_high;
        int pageset_batch;

#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 */

        /* 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);
         *
         * present_early_pages is present pages existing within the zone
         * located on memory available since early boot, excluding hotplugged
         * memory.
         *
         * 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;
         *
         * cma pages is present pages that are assigned for CMA use
         * (MIGRATE_CMA).
         *
         * 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
         * mem_hotplug_begin/end(). Any reader who can't tolerant drift of
         * present_pages should get_online_mems() to get a stable value.
         */
        atomic_long_t           managed_pages;
        unsigned long           spanned_pages;
        unsigned long           present_pages;
#if defined(CONFIG_MEMORY_HOTPLUG)
        unsigned long           present_early_pages;
#endif
#ifdef CONFIG_CMA
        unsigned long           cma_pages;
#endif

        const char              *name;

#ifdef CONFIG_MEMORY_ISOLATION
        /*
         * Number of isolated pageblock. It is used to solve incorrect
         * freepage counting problem due to racy retrieving migratetype
         * of pageblock. Protected by zone->lock.
         */
        unsigned long           nr_isolate_pageblock;
#endif

#ifdef CONFIG_MEMORY_HOTPLUG
        /* see spanned/present_pages for more description */
        seqlock_t               span_seqlock;
#endif

        int initialized;

        /* Write-intensive fields used from the page allocator */
        ZONE_PADDING(_pad1_)

        /* free areas of different sizes */
        struct free_area        free_area[MAX_ORDER];

        /* zone flags, see below */
        unsigned long           flags;

        /* Primarily protects free_area */
        spinlock_t              lock;

        /* Write-intensive fields used by compaction and vmstats. */
        ZONE_PADDING(_pad2_)

        /*
         * 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;

#if defined CONFIG_COMPACTION || defined CONFIG_CMA
        /* pfn where compaction free scanner should start */
        unsigned long           compact_cached_free_pfn;
        /* pfn where compaction migration scanner should start */
        unsigned long           compact_cached_migrate_pfn[ASYNC_AND_SYNC];
        unsigned long           compact_init_migrate_pfn;
        unsigned long           compact_init_free_pfn;
#endif

#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.
         * compact_order_failed is the minimum compaction failed order.
         */
        unsigned int            compact_considered;
        unsigned int            compact_defer_shift;
        int                     compact_order_failed;
#endif

#if defined CONFIG_COMPACTION || defined CONFIG_CMA
        /* Set to true when the PG_migrate_skip bits should be cleared */
        bool                    compact_blockskip_flush;
#endif

        bool                    contiguous;

        ZONE_PADDING(_pad3_)
        /* Zone statistics */
        atomic_long_t           vm_stat[NR_VM_ZONE_STAT_ITEMS];
        atomic_long_t           vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
} ____cacheline_internodealigned_in_smp;

enum pgdat_flags {
        PGDAT_DIRTY,                    /* reclaim scanning has recently found
                                         * many dirty file pages at the tail
                                         * of the LRU.
                                         */
        PGDAT_WRITEBACK,                /* reclaim scanning has recently found
                                         * many pages under writeback
                                         */
        PGDAT_RECLAIM_LOCKED,           /* prevents concurrent reclaim */
};

enum zone_flags {
        ZONE_BOOSTED_WATERMARK,         /* zone recently boosted watermarks.
                                         * Cleared when kswapd is woken.
                                         */
        ZONE_RECLAIM_ACTIVE,            /* kswapd may be scanning the zone. */
};

static inline unsigned long zone_managed_pages(struct zone *zone)
{
        return (unsigned long)atomic_long_read(&zone->managed_pages);
}

static inline unsigned long zone_cma_pages(struct zone *zone)
{
#ifdef CONFIG_CMA
        return zone->cma_pages;
#else
        return 0;
#endif
}

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->initialized;
}

static inline bool zone_is_empty(struct zone *zone)
{
        return zone->spanned_pages == 0;
}

/*
 * Return true if [start_pfn, start_pfn + nr_pages) range has a non-empty
 * intersection with the given zone
 */
static inline bool zone_intersects(struct zone *zone,
                unsigned long start_pfn, unsigned long nr_pages)
{
        if (zone_is_empty(zone))
                return false;
        if (start_pfn >= zone_end_pfn(zone) ||
            start_pfn + nr_pages <= zone->zone_start_pfn)
                return false;

        return true;
}

/*
 * 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)

enum {
        ZONELIST_FALLBACK,      /* zonelist with fallback */
#ifdef CONFIG_NUMA
        /*
         * The NUMA zonelists are doubled because we need zonelists that
         * restrict the allocations to a single node for __GFP_THISNODE.
         */
        ZONELIST_NOFALLBACK,    /* zonelist without fallback (__GFP_THISNODE) */
#endif
        MAX_ZONELISTS
};

/*
 * 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.
 *
 * 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 zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
};

/*
 * The array of struct pages for flatmem.
 * It must be declared for SPARSEMEM as well because there are configurations
 * that rely on that.
 */
extern struct page *mem_map;

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
struct deferred_split {
        spinlock_t split_queue_lock;
        struct list_head split_queue;
        unsigned long split_queue_len;
};
#endif

/*
 * On NUMA machines, each NUMA node would have a pg_data_t to describe
 * it's memory layout. On UMA machines there is a single pglist_data which
 * describes the whole memory.
 *
 * Memory statistics and page replacement data structures are maintained on a
 * per-zone basis.
 */
typedef struct pglist_data {
        /*
         * node_zones contains just the zones for THIS node. Not all of the
         * zones may be populated, but it is the full list. It is referenced by
         * this node's node_zonelists as well as other node's node_zonelists.
         */
        struct zone node_zones[MAX_NR_ZONES];

        /*
         * node_zonelists contains references to all zones in all nodes.
         * Generally the first zones will be references to this node's
         * node_zones.
         */
        struct zonelist node_zonelists[MAX_ZONELISTS];

        int nr_zones; /* number of populated zones in this node */
#ifdef CONFIG_FLATMEM   /* means !SPARSEMEM */
        struct page *node_mem_map;
#ifdef CONFIG_PAGE_EXTENSION
        struct page_ext *node_page_ext;
#endif
#endif
#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT)
        /*
         * Must be held any time you expect node_start_pfn,
         * node_present_pages, node_spanned_pages or nr_zones to stay constant.
         * Also synchronizes pgdat->first_deferred_pfn during deferred page
         * init.
         *
         * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
         * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG
         * or CONFIG_DEFERRED_STRUCT_PAGE_INIT.
         *
         * 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;
        wait_queue_head_t kswapd_wait;
        wait_queue_head_t pfmemalloc_wait;

        /* workqueues for throttling reclaim for different reasons. */
        wait_queue_head_t reclaim_wait[NR_VMSCAN_THROTTLE];

        atomic_t nr_writeback_throttled;/* nr of writeback-throttled tasks */
        unsigned long nr_reclaim_start; /* nr pages written while throttled
                                         * when throttling started. */
        struct task_struct *kswapd;     /* Protected by
                                           mem_hotplug_begin/end() */
        int kswapd_order;
        enum zone_type kswapd_highest_zoneidx;

        int kswapd_failures;            /* Number of 'reclaimed == 0' runs */

#ifdef CONFIG_COMPACTION
        int kcompactd_max_order;
        enum zone_type kcompactd_highest_zoneidx;
        wait_queue_head_t kcompactd_wait;
        struct task_struct *kcompactd;
        bool proactive_compact_trigger;
#endif
        /*
         * This is a per-node reserve of pages that are not available
         * to userspace allocations.
         */
        unsigned long           totalreserve_pages;

#ifdef CONFIG_NUMA
        /*
         * node reclaim becomes active if more unmapped pages exist.
         */
        unsigned long           min_unmapped_pages;
        unsigned long           min_slab_pages;
#endif /* CONFIG_NUMA */

        /* Write-intensive fields used by page reclaim */
        ZONE_PADDING(_pad1_)

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
        /*
         * If memory initialisation on large machines is deferred then this
         * is the first PFN that needs to be initialised.
         */
        unsigned long first_deferred_pfn;
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        struct deferred_split deferred_split_queue;
#endif

        /* Fields commonly accessed by the page reclaim scanner */

        /*
         * NOTE: THIS IS UNUSED IF MEMCG IS ENABLED.
         *
         * Use mem_cgroup_lruvec() to look up lruvecs.
         */
        struct lruvec           __lruvec;

        unsigned long           flags;

        ZONE_PADDING(_pad2_)

        /* Per-node vmstats */
        struct per_cpu_nodestat __percpu *per_cpu_nodestats;
        atomic_long_t           vm_stat[NR_VM_NODE_STAT_ITEMS];
} 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_FLATMEM
#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>

void build_all_zonelists(pg_data_t *pgdat);
void wakeup_kswapd(struct zone *zone, gfp_t gfp_mask, int order,
                   enum zone_type highest_zoneidx);
bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
                         int highest_zoneidx, unsigned int alloc_flags,
                         long free_pages);
bool zone_watermark_ok(struct zone *z, unsigned int order,
                unsigned long mark, int highest_zoneidx,
                unsigned int alloc_flags);
bool zone_watermark_ok_safe(struct zone *z, unsigned int order,
                unsigned long mark, int highest_zoneidx);
/*
 * Memory initialization context, use to differentiate memory added by
 * the platform statically or via memory hotplug interface.
 */
enum meminit_context {
        MEMINIT_EARLY,
        MEMINIT_HOTPLUG,
};

extern void init_currently_empty_zone(struct zone *zone, unsigned long start_pfn,
                                     unsigned long size);

extern void lruvec_init(struct lruvec *lruvec);

static inline struct pglist_data *lruvec_pgdat(struct lruvec *lruvec)
{
#ifdef CONFIG_MEMCG
        return lruvec->pgdat;
#else
        return container_of(lruvec, struct pglist_data, __lruvec);
#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

/*
 * 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)

#ifdef CONFIG_ZONE_DEVICE
static inline bool zone_is_zone_device(struct zone *zone)
{
        return zone_idx(zone) == ZONE_DEVICE;
}
#else
static inline bool zone_is_zone_device(struct zone *zone)
{
        return false;
}
#endif

/*
 * Returns true if a zone has pages managed by the buddy allocator.
 * All the reclaim decisions have to use this function rather than
 * populated_zone(). If the whole zone is reserved then we can easily
 * end up with populated_zone() && !managed_zone().
 */
static inline bool managed_zone(struct zone *zone)
{
        return zone_managed_pages(zone);
}

/* Returns true if a zone has memory */
static inline bool populated_zone(struct zone *zone)
{
        return zone->present_pages;
}

#ifdef CONFIG_NUMA
static inline int zone_to_nid(struct zone *zone)
{
        return zone->node;
}

static inline void zone_set_nid(struct zone *zone, int nid)
{
        zone->node = nid;
}
#else
static inline int zone_to_nid(struct zone *zone)
{
        return 0;
}

static inline void zone_set_nid(struct zone *zone, int nid) {}
#endif

extern int movable_zone;

static inline int is_highmem_idx(enum zone_type idx)
{
#ifdef CONFIG_HIGHMEM
        return (idx == ZONE_HIGHMEM ||
                (idx == ZONE_MOVABLE && movable_zone == ZONE_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
 * Return: 1 for a highmem zone, 0 otherwise
 */
static inline int is_highmem(struct zone *zone)
{
#ifdef CONFIG_HIGHMEM
        return is_highmem_idx(zone_idx(zone));
#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 *, size_t *,
                loff_t *);
int watermark_scale_factor_sysctl_handler(struct ctl_table *, int, void *,
                size_t *, loff_t *);
extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES];
int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int, void *,
                size_t *, loff_t *);
int percpu_pagelist_high_fraction_sysctl_handler(struct ctl_table *, int,
                void *, size_t *, loff_t *);
int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
                void *, size_t *, loff_t *);
int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
                void *, size_t *, loff_t *);
int numa_zonelist_order_handler(struct ctl_table *, int,
                void *, size_t *, loff_t *);
extern int percpu_pagelist_high_fraction;
extern char numa_zonelist_order[];
#define NUMA_ZONELIST_ORDER_LEN 16

#ifndef CONFIG_NUMA

extern struct pglist_data contig_page_data;
static inline struct pglist_data *NODE_DATA(int nid)
{
        return &contig_page_data;
}
#define NODE_MEM_MAP(nid)       mem_map

#else /* CONFIG_NUMA */

#include <asm/mmzone.h>

#endif /* !CONFIG_NUMA */

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)
{
        return zone_to_nid(zoneref->zone);
}

struct zoneref *__next_zones_zonelist(struct zoneref *z,
                                        enum zone_type highest_zoneidx,
                                        nodemask_t *nodes);

/**
 * 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
 *
 * 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.
 *
 * Return: the next zone at or below highest_zoneidx within the allowed
 * nodemask using a cursor within a zonelist as a starting point
 */
static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
                                        enum zone_type highest_zoneidx,
                                        nodemask_t *nodes)
{
        if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))
                return z;
        return __next_zones_zonelist(z, highest_zoneidx, nodes);
}

/**
 * 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
 *
 * 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.
 *
 * When no eligible zone is found, zoneref->zone is NULL (zoneref itself is
 * never NULL). This may happen either genuinely, or due to concurrent nodemask
 * update due to cpuset modification.
 *
 * Return: Zoneref pointer for the first suitable zone found
 */
static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
                                        enum zone_type highest_zoneidx,
                                        nodemask_t *nodes)
{
        return next_zones_zonelist(zonelist->_zonerefs,
                                                        highest_zoneidx, nodes);
}

/**
 * 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->_zonerefs 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 = zonelist_zone(z);       \
                zone;                                                   \
                z = next_zones_zonelist(++z, highidx, nodemask),        \
                        zone = zonelist_zone(z))

#define for_next_zone_zonelist_nodemask(zone, z, highidx, nodemask) \
        for (zone = z->zone;    \
                zone;                                                   \
                z = next_zones_zonelist(++z, highidx, nodemask),        \
                        zone = zonelist_zone(z))


/**
 * 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)

/* Whether the 'nodes' are all movable nodes */
static inline bool movable_only_nodes(nodemask_t *nodes)
{
        struct zonelist *zonelist;
        struct zoneref *z;
        int nid;

        if (nodes_empty(*nodes))
                return false;

        /*
         * We can chose arbitrary node from the nodemask to get a
         * zonelist as they are interlinked. We just need to find
         * at least one zone that can satisfy kernel allocations.
         */
        nid = first_node(*nodes);
        zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
        z = first_zones_zonelist(zonelist, ZONE_NORMAL, nodes);
        return (!z->zone) ? true : false;
}


#ifdef CONFIG_SPARSEMEM
#include <asm/sparsemem.h>
#endif

#ifdef CONFIG_FLATMEM
#define pfn_to_nid(pfn)         (0)
#endif

#ifdef CONFIG_SPARSEMEM

/*
 * 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

static inline unsigned long pfn_to_section_nr(unsigned long pfn)
{
        return pfn >> PFN_SECTION_SHIFT;
}
static inline unsigned long section_nr_to_pfn(unsigned long sec)
{
        return 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)

#define SUBSECTION_SHIFT 21
#define SUBSECTION_SIZE (1UL << SUBSECTION_SHIFT)

#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

#define SUBSECTION_ALIGN_UP(pfn) ALIGN((pfn), PAGES_PER_SUBSECTION)
#define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)

struct mem_section_usage {
#ifdef CONFIG_SPARSEMEM_VMEMMAP
        DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
#endif
        /* See declaration of similar field in struct zone */
        unsigned long pageblock_flags[0];
};

void subsection_map_init(unsigned long pfn, unsigned long nr_pages);

struct page;
struct page_ext;
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;

        struct mem_section_usage *usage;
#ifdef CONFIG_PAGE_EXTENSION
        /*
         * If SPARSEMEM, pgdat doesn't have page_ext pointer. We use
         * section. (see page_ext.h about this.)
         */
        struct page_ext *page_ext;
        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;
#else
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
        if (!mem_section)
                return NULL;
#endif
        if (!mem_section[SECTION_NR_TO_ROOT(nr)])
                return NULL;
        return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
}
extern size_t mem_section_usage_size(void);

/*
 * We use the lower bits of the mem_map pointer to store
 * a little bit of information.  The pointer is calculated
 * as mem_map - section_nr_to_pfn(pnum).  The result is
 * aligned to the minimum alignment of the two values:
 *   1. All mem_map arrays are page-aligned.
 *   2. section_nr_to_pfn() always clears PFN_SECTION_SHIFT
 *      lowest bits.  PFN_SECTION_SHIFT is arch-specific
 *      (equal SECTION_SIZE_BITS - PAGE_SHIFT), and the
 *      worst combination is powerpc with 256k pages,
 *      which results in PFN_SECTION_SHIFT equal 6.
 * To sum it up, at least 6 bits are available.
 */
#define SECTION_MARKED_PRESENT          (1UL<<0)
#define SECTION_HAS_MEM_MAP             (1UL<<1)
#define SECTION_IS_ONLINE               (1UL<<2)
#define SECTION_IS_EARLY                (1UL<<3)
#define SECTION_TAINT_ZONE_DEVICE       (1UL<<4)
#define SECTION_MAP_LAST_BIT            (1UL<<5)
#define SECTION_MAP_MASK                (~(SECTION_MAP_LAST_BIT-1))
#define SECTION_NID_SHIFT               6

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 early_section(struct mem_section *section)
{
        return (section && (section->section_mem_map & SECTION_IS_EARLY));
}

static inline int valid_section_nr(unsigned long nr)
{
        return valid_section(__nr_to_section(nr));
}

static inline int online_section(struct mem_section *section)
{
        return (section && (section->section_mem_map & SECTION_IS_ONLINE));
}

static inline int online_device_section(struct mem_section *section)
{
        unsigned long flags = SECTION_IS_ONLINE | SECTION_TAINT_ZONE_DEVICE;

        return section && ((section->section_mem_map & flags) == flags);
}

static inline int online_section_nr(unsigned long nr)
{
        return online_section(__nr_to_section(nr));
}

#ifdef CONFIG_MEMORY_HOTPLUG
void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
#endif

static inline struct mem_section *__pfn_to_section(unsigned long pfn)
{
        return __nr_to_section(pfn_to_section_nr(pfn));
}

extern unsigned long __highest_present_section_nr;

static inline int subsection_map_index(unsigned long pfn)
{
        return (pfn & ~(PAGE_SECTION_MASK)) / PAGES_PER_SUBSECTION;
}

#ifdef CONFIG_SPARSEMEM_VMEMMAP
static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
{
        int idx = subsection_map_index(pfn);

        return test_bit(idx, ms->usage->subsection_map);
}
#else
static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
{
        return 1;
}
#endif

#ifndef CONFIG_HAVE_ARCH_PFN_VALID
/**
 * pfn_valid - check if there is a valid memory map entry for a PFN
 * @pfn: the page frame number to check
 *
 * Check if there is a valid memory map entry aka struct page for the @pfn.
 * Note, that availability of the memory map entry does not imply that
 * there is actual usable memory at that @pfn. The struct page may
 * represent a hole or an unusable page frame.
 *
 * Return: 1 for PFNs that have memory map entries and 0 otherwise
 */
static inline int pfn_valid(unsigned long pfn)
{
        struct mem_section *ms;

        /*
         * Ensure the upper PAGE_SHIFT bits are clear in the
         * pfn. Else it might lead to false positives when
         * some of the upper bits are set, but the lower bits
         * match a valid pfn.
         */
        if (PHYS_PFN(PFN_PHYS(pfn)) != pfn)
                return 0;

        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
                return 0;
        ms = __pfn_to_section(pfn);
        if (!valid_section(ms))
                return 0;
        /*
         * Traditionally early sections always returned pfn_valid() for
         * the entire section-sized span.
         */
        return early_section(ms) || pfn_section_valid(ms, pfn);
}
#endif

static inline int pfn_in_present_section(unsigned long pfn)
{
        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
                return 0;
        return present_section(__pfn_to_section(pfn));
}

static inline unsigned long next_present_section_nr(unsigned long section_nr)
{
        while (++section_nr <= __highest_present_section_nr) {
                if (present_section_nr(section_nr))
                        return section_nr;
        }

        return -1;
}

/*
 * 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

void sparse_init(void);
#else
#define sparse_init()   do {} while (0)
#define sparse_index_init(_sec, _nid)  do {} while (0)
#define pfn_in_present_section pfn_valid
#define subsection_map_init(_pfn, _nr_pages) do {} while (0)
#endif /* CONFIG_SPARSEMEM */

#endif /* !__GENERATING_BOUNDS.H */
#endif /* !__ASSEMBLY__ */
#endif /* _LINUX_MMZONE_H */