内存管理相关数据结构之pg_data_t

承接内存管理相关概念讲解相关数据结构。
主要有

• pg_data_t: 表示节点；
• zone： 内存域；
• page: 页帧；

pglist_data定义如下：

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_PAGE_EXTENSION
    struct page_ext *node_page_ext;
#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;
    wait_queue_head_t kswapd_wait;
    wait_queue_head_t pfmemalloc_wait;
    struct task_struct *kswapd; /* Protected by
                       mem_hotplug_begin/end() */
    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

#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;
    /* Number of non-deferred pages */
    unsigned long static_init_pgcnt;
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
} pg_data_t;

• node_zones是一个数组，包含节点中各内存域(ZONE_DMA, ZONE_DMA32, ZONE_NORMAL...)的数据结构;
• node_zonelists指定了节点的备用列表；
• nr_zones 指示了节点中不同内存域数目；
• node_mem_map描述节点的所有物理内存页面。包含节点的所有内存域；
• bdata 系统启动自举内存分配器数据结构实例；
• node_start_pfn 当前NUMA节点第一页帧逻辑编号。在UMA总是0.
• node_present_pages节点中页帧的数目；
• node_spanned_pages节点以页帧为单位计算的数目。由于空洞的存在可能不等于node_present_pages，应该是大于等于node_present_pages；
• node_id是全局节点ID；
• kswapd_wait：node的等待队列，交换守护列队进程的等待列表
• kswapd_max_order：需要释放的区域的长度，以页阶为单位

若系统节点多余一个，则内核会维护一个位图用于提供每个节点的状态信息，状态信息为一个enum。定义如下:

enum node_states {
    N_POSSIBLE,     /* The node could become online at some point */
    N_ONLINE,       /* The node is online */
    N_NORMAL_MEMORY,    /* The node has regular memory */
#ifdef CONFIG_HIGHMEM
    N_HIGH_MEMORY,      /* The node has regular or high memory */
#else
    N_HIGH_MEMORY = N_NORMAL_MEMORY,
#endif
#ifdef CONFIG_MOVABLE_NODE
    N_MEMORY,       /* The node has memory(regular, high, movable) */
#else
    N_MEMORY = N_HIGH_MEMORY,
#endif
    N_CPU,      /* The node has one or more cpus */
    NR_NODE_STATES
};