記憶體管理相關數據結構之pg_data_t

承接記憶體管理相關概念講解相關數據結構。主要有

• pg_data_t: 表示節點；
• zone： 記憶體域；
• page: 頁幀；

pglist_data定義如下：

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是一個數組，包含節點中各記憶體域(ZONE_DMA, ZONE_DMA32, ZONE_NORMAL...)的數據結構;
• node_zonelists指定了節點的備用列表；
• nr_zones 指示了節點中不同記憶體域數目；
• node_mem_map描述節點的所有物理記憶體頁面。包含節點的所有記憶體域；
• bdata 系統啟動自舉記憶體分配器數據結構實例；
• node_start_pfn 當前NUMA節點第一頁幀邏輯編號。在UMA總是0.
• node_present_pages節點中頁幀的數目；
• node_spanned_pages節點以頁幀為單位計算的數目。由於空洞的存在可能不等於node_present_pages，應該是大於等於node_present_pages；
• node_id是全局節點ID；
• kswapd_wait：node的等待隊列，交換守護列隊進程的等待列表
• kswapd_max_order：需要釋放的區域的長度，以頁階為單位

若系統節點多餘一個，則內核會維護一個點陣圖用於提供每個節點的狀態信息，狀態信息為一個enum。定義如下:

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
};