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分类: LINUX

2015-12-18 15:50:44

前面已经分析了内存管理框架的构建实现过程,有部分内容未完全呈现出来,这里主要做个补充。

如下图,这是前面已经看到过的linux物理内存管理框架的层次关系。


现着重分析一下各个管理结构体的成员功能作用。

  1. 【file:/include/linux/mmzone.h】
  2. typedef struct pglist_data {
  3.     struct zone node_zones[MAX_NR_ZONES];
  4.     struct zonelist node_zonelists[MAX_ZONELISTS];
  5.     int nr_zones;
  6. #ifdef CONFIG_FLAT_NODE_MEM_MAP /* means !SPARSEMEM */
  7.     struct page *node_mem_map;
  8. #ifdef CONFIG_MEMCG
  9.     struct page_cgroup *node_page_cgroup;
  10. #endif
  11. #endif
  12. #ifndef CONFIG_NO_BOOTMEM
  13.     struct bootmem_data *bdata;
  14. #endif
  15. #ifdef CONFIG_MEMORY_HOTPLUG
  16.     /*
  17.      * Must be held any time you expect node_start_pfn, node_present_pages
  18.      * or node_spanned_pages stay constant. Holding this will also
  19.      * guarantee that any pfn_valid() stays that way.
  20.      *
  21.      * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
  22.      * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG.
  23.      *
  24.      * Nests above zone->lock and zone->span_seqlock
  25.      */
  26.     spinlock_t node_size_lock;
  27. #endif
  28.     unsigned long node_start_pfn;
  29.     unsigned long node_present_pages; /* total number of physical pages */
  30.     unsigned long node_spanned_pages; /* total size of physical page
  31.                          range, including holes */
  32.     int node_id;
  33.     nodemask_t reclaim_nodes; /* Nodes allowed to reclaim from */
  34.     wait_queue_head_t kswapd_wait;
  35.     wait_queue_head_t pfmemalloc_wait;
  36.     struct task_struct *kswapd; /* Protected by lock_memory_hotplug() */
  37.     int kswapd_max_order;
  38.     enum zone_type classzone_idx;
  39. #ifdef CONFIG_NUMA_BALANCING
  40.     /* Lock serializing the migrate rate limiting window */
  41.     spinlock_t numabalancing_migrate_lock;
  42.  
  43.     /* Rate limiting time interval */
  44.     unsigned long numabalancing_migrate_next_window;
  45.  
  46.     /* Number of pages migrated during the rate limiting time interval */
  47.     unsigned long numabalancing_migrate_nr_pages;
  48. #endif
  49. } pg_data_t;

truct zone node_zones[MAX_NR_ZONES];

——存放该pg_data_t里面的zone

struct zonelist node_zonelists[MAX_ZONELISTS];

——其用于管理备用节点及内存域的列表,该列表表示内存分配策略。该链表将node_zones串联起来,其串联zone的顺序就是各区的内存申请顺序,例如normal->dma->highmem,申请时也将会是先从normal区中申请,如果申请不到,再依序到从dma区、highmem区去申请;

int nr_zones;

——用于记录zone的个数;

struct page *node_mem_map;

——其指向一个page结构的数组,数组中的每个成员为该节点中的一个物理页面,于是整个数组就对应了该节点中所有的物理页面;

struct page_cgroup *node_page_cgroup;

——用于管理page_cgroup,原来的page_cgrouppage页面管理结构的一个成员,现在移到这里了,它将会在初始化时所有的page_cgroup都将申请下来;

struct bootmem_data *bdata;

——该数据指向bootmem_node_data,可以通过system.map查到。原是用于bootmem内存分配器的信息存储,当前改用memblock算法,则不存在该成员;

unsigned long node_start_pfn;

——指向当前pg_data_t结构管理的物理起始页面;

unsigned long node_present_pages;

——记录物理页面数总量,除开内存空洞的物理页面数;

unsigned long node_spanned_pages;

——最大和最小页面号的差值,包括内存空洞的总的物理页面大小;

int node_id;

——pg_data_t对应的索引号,非NUMA架构下该值为0

nodemask_t reclaim_nodes;

——用于记录可回收的内存管理节点node信息;

wait_queue_head_t kswapd_wait;

——kswapd是页面交换守护线程,该线程会阻塞在这个等待队列,当满足条件后,调用wake_up_interruptible()唤醒该队列进行相关操作;

wait_queue_head_t pfmemalloc_wait;

——用于减缓内存直接回收;

struct task_struct *kswapd;

——指向kswapd守护线程的任务指针;

int kswapd_max_order;

——用于表示kswapd守护线程每次回收的页面个数;

enum zone_type classzone_idx;

——该成员与kswapd有关;

  1. 【file:/include/linux/mmzone.h】
  2. struct zone {
  3.     /* Fields commonly accessed by the page allocator */
  4.  
  5.     /* zone watermarks, access with *_wmark_pages(zone) macros */
  6.     unsigned long watermark[NR_WMARK];
  7.  
  8.     /*
  9.      * When free pages are below this point, additional steps are taken
  10.      * when reading the number of free pages to avoid per-cpu counter
  11.      * drift allowing watermarks to be breached
  12.      */
  13.     unsigned long percpu_drift_mark;
  14.  
  15.     /*
  16.      * We don't know if the memory that we're going to allocate will be freeable
  17.      * or/and it will be released eventually, so to avoid totally wasting several
  18.      * GB of ram we must reserve some of the lower zone memory (otherwise we risk
  19.      * to run OOM on the lower zones despite there's tons of freeable ram
  20.      * on the higher zones). This array is recalculated at runtime if the
  21.      * sysctl_lowmem_reserve_ratio sysctl changes.
  22.      */
  23.     unsigned long lowmem_reserve[MAX_NR_ZONES];
  24.  
  25.     /*
  26.      * This is a per-zone reserve of pages that should not be
  27.      * considered dirtyable memory.
  28.      */
  29.     unsigned long dirty_balance_reserve;
  30.  
  31. #ifdef CONFIG_NUMA
  32.     int node;
  33.     /*
  34.      * zone reclaim becomes active if more unmapped pages exist.
  35.      */
  36.     unsigned long min_unmapped_pages;
  37.     unsigned long min_slab_pages;
  38. #endif
  39.     struct per_cpu_pageset __percpu *pageset;
  40.     /*
  41.      * free areas of different sizes
  42.      */
  43.     spinlock_t lock;
  44. #if defined CONFIG_COMPACTION || defined CONFIG_CMA
  45.     /* Set to true when the PG_migrate_skip bits should be cleared */
  46.     bool compact_blockskip_flush;
  47.  
  48.     /* pfns where compaction scanners should start */
  49.     unsigned long compact_cached_free_pfn;
  50.     unsigned long compact_cached_migrate_pfn;
  51. #endif
  52. #ifdef CONFIG_MEMORY_HOTPLUG
  53.     /* see spanned/present_pages for more description */
  54.     seqlock_t span_seqlock;
  55. #endif
  56.     struct free_area free_area[MAX_ORDER];
  57.  
  58. #ifndef CONFIG_SPARSEMEM
  59.     /*
  60.      * Flags for a pageblock_nr_pages block. See pageblock-flags.h.
  61.      * In SPARSEMEM, this map is stored in struct mem_section
  62.      */
  63.     unsigned long *pageblock_flags;
  64. #endif /* CONFIG_SPARSEMEM */
  65.  
  66. #ifdef CONFIG_COMPACTION
  67.     /*
  68.      * On compaction failure, 1<<compact_defer_shift compactions
  69.      * are skipped before trying again. The number attempted since
  70.      * last failure is tracked with compact_considered.
  71.      */
  72.     unsigned int compact_considered;
  73.     unsigned int compact_defer_shift;
  74.     int compact_order_failed;
  75. #endif
  76.  
  77.     ZONE_PADDING(_pad1_)
  78.  
  79.     /* Fields commonly accessed by the page reclaim scanner */
  80.     spinlock_t lru_lock;
  81.     struct lruvec lruvec;
  82.  
  83.     unsigned long pages_scanned; /* since last reclaim */
  84.     unsigned long flags; /* zone flags, see below */
  85.  
  86.     /* Zone statistics */
  87.     atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
  88.  
  89.     /*
  90.      * The target ratio of ACTIVE_ANON to INACTIVE_ANON pages on
  91.      * this zone's LRU. Maintained by the pageout code.
  92.      */
  93.     unsigned int inactive_ratio;
  94.  
  95.  
  96.     ZONE_PADDING(_pad2_)
  97.     /* Rarely used or read-mostly fields */
  98.  
  99.     /*
  100.      * wait_table -- the array holding the hash table
  101.      * wait_table_hash_nr_entries -- the size of the hash table array
  102.      * wait_table_bits -- wait_table_size == (1 << wait_table_bits)
  103.      *
  104.      * The purpose of all these is to keep track of the people
  105.      * waiting for a page to become available and make them
  106.      * runnable again when possible. The trouble is that this
  107.      * consumes a lot of space, especially when so few things
  108.      * wait on pages at a given time. So instead of using
  109.      * per-page waitqueues, we use a waitqueue hash table.
  110.      *
  111.      * The bucket discipline is to sleep on the same queue when
  112.      * colliding and wake all in that wait queue when removing.
  113.      * When something wakes, it must check to be sure its page is
  114.      * truly available, a la thundering herd. The cost of a
  115.      * collision is great, but given the expected load of the
  116.      * table, they should be so rare as to be outweighed by the
  117.      * benefits from the saved space.
  118.      *
  119.      * __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the
  120.      * primary users of these fields, and in mm/page_alloc.c
  121.      * free_area_init_core() performs the initialization of them.
  122.      */
  123.     wait_queue_head_t * wait_table;
  124.     unsigned long wait_table_hash_nr_entries;
  125.     unsigned long wait_table_bits;
  126.  
  127.     /*
  128.      * Discontig memory support fields.
  129.      */
  130.     struct pglist_data *zone_pgdat;
  131.     /* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
  132.     unsigned long zone_start_pfn;
  133.  
  134.     /*
  135.      * spanned_pages is the total pages spanned by the zone, including
  136.      * holes, which is calculated as:
  137.      * spanned_pages = zone_end_pfn - zone_start_pfn;
  138.      *
  139.      * present_pages is physical pages existing within the zone, which
  140.      * is calculated as:
  141.      * present_pages = spanned_pages - absent_pages(pages in holes);
  142.      *
  143.      * managed_pages is present pages managed by the buddy system, which
  144.      * is calculated as (reserved_pages includes pages allocated by the
  145.      * bootmem allocator):
  146.      * managed_pages = present_pages - reserved_pages;
  147.      *
  148.      * So present_pages may be used by memory hotplug or memory power
  149.      * management logic to figure out unmanaged pages by checking
  150.      * (present_pages - managed_pages). And managed_pages should be used
  151.      * by page allocator and vm scanner to calculate all kinds of watermarks
  152.      * and thresholds.
  153.      *
  154.      * Locking rules:
  155.      *
  156.      * zone_start_pfn and spanned_pages are protected by span_seqlock.
  157.      * It is a seqlock because it has to be read outside of zone->lock,
  158.      * and it is done in the main allocator path. But, it is written
  159.      * quite infrequently.
  160.      *
  161.      * The span_seq lock is declared along with zone->lock because it is
  162.      * frequently read in proximity to zone->lock. It's good to
  163.      * give them a chance of being in the same cacheline.
  164.      *
  165.      * Write access to present_pages at runtime should be protected by
  166.      * lock_memory_hotplug()/unlock_memory_hotplug(). Any reader who can't
  167.      * tolerant drift of present_pages should hold memory hotplug lock to
  168.      * get a stable value.
  169.      *
  170.      * Read access to managed_pages should be safe because it's unsigned
  171.      * long. Write access to zone->managed_pages and totalram_pages are
  172.      * protected by managed_page_count_lock at runtime. Idealy only
  173.      * adjust_managed_page_count() should be used instead of directly
  174.      * touching zone->managed_pages and totalram_pages.
  175.      */
  176.     unsigned long spanned_pages;
  177.     unsigned long present_pages;
  178.     unsigned long managed_pages;
  179.  
  180.     /*
  181.      * Number of MIGRATE_RESEVE page block. To maintain for just
  182.      * optimization. Protected by zone->lock.
  183.      */
  184.     int nr_migrate_reserve_block;
  185.  
  186.     /*
  187.      * rarely used fields:
  188.      */
  189.     const char *name;
  190. } ____cacheline_internodealigned_in_smp;

unsigned long watermark[NR_WMARK];

——该数组有三个值WMARK_MINWMARK_LOWWMARK_HIGH,如命名所标识,min最小,low居中,high最大。内存分配过程中,当空闲页面达到low时,内存分配器会唤醒kswapd守护进程来回收物理页面;当空闲页面达到min时,内存分配器就会唤醒kswapd以同步方式回收;如果kswapd被唤醒后,空闲页面达到high时,则会使kswapd再次休眠;

unsigned long percpu_drift_mark;

——当空闲页面低于该值,将会引发附加操作的执行,用于避免前面的watermark被冲破;

unsigned long lowmem_reserve[MAX_NR_ZONES];

——记录每个管理区中必须保留的物理页面数,以用于紧急状况下的内存分配;

unsigned long dirty_balance_reserve;

——用于表示不会被内存分配器分配出去的空闲页面部分的近似值;

struct per_cpu_pageset __percpu *pageset;

——该数组里面的成员pcp用于实现冷热页面的管理;

spinlock_t lock;

——spinlock锁,用于解决该管理区的并发问题;

struct free_area free_area[MAX_ORDER];

——主要用于Buddy内存管理算法(伙伴算法);

unsigned long *pageblock_flags;

——与伙伴算法的碎片迁移算法有关;

spinlock_t lru_lock;

——用于保护lruvec结构数据;

struct lruvec lruvec;

——lruvec该数组里面有一个lists是用于lru管理的链表,另外有一个reclaim_stat用于页面回收的状态标示;

unsigned long pages_scanned;

——用于记录上次物理页面回收时,扫描过的页描述符总数;

unsigned long flags;

——用于表示当前内存管理区的状态;

atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];

——用于统计该内存管理区中各项状态的数值;

unsigned int inactive_ratio;

——不活跃的页面比例;

wait_queue_head_t *wait_table;

unsigned long wait_table_hash_nr_entries;

unsigned long wait_table_bits;

——当多个进程同时访问同一页面时,必然会有进程先行访问操作,此时该页面不可用,因此其他的则需阻塞等待。当页面不可用时,则会将页面进行hash运算加入到该管理区wait_table的哈希表中,当页面可用时将会把里面任务列表中等待的进程进行唤醒。如果存在多个页面有相同的hash值,那么这些等待不同页面的任务仍然会睡眠在同一个hash表节点下,当相同hash值的某个页面可用时,将会唤醒所有进程,当进程在唤醒时需要检查是否是自己所等待的页面。其中wait_table_hash_nr_entries表示该哈希表中等待队列的数量,

struct pglist_data  *zone_pgdat;

——指向该内存管理区的pg_data_list

unsigned long zone_start_pfn;

——记录当前内存管理区中最小的物理页面号;

unsigned long spanned_pages;

——记录内存管理区的总页面数,包括内存空洞的页面数,实则上是管理区末尾页面号和起始页面号的差值;

unsigned long present_pages;

——除去内存空洞后的内存管理区实际有效的总页面数;

unsigned long managed_pages;

——用于记录被内存管理算法管理的物理页面数,这是除去了在初始化阶段被申请的页面;

int nr_migrate_reserve_block;

——用于优化的,记录内存迁移保留的页面数;

const char *name;

——用于记录该管理区的名字;

  1. 【file:/include/linux/mmzone.h】
  2. /*
  3.  * Each physical page in the system has a struct page associated with
  4.  * it to keep track of whatever it is we are using the page for at the
  5.  * moment. Note that we have no way to track which tasks are using
  6.  * a page, though if it is a pagecache page, rmap structures can tell us
  7.  * who is mapping it.
  8.  *
  9.  * The objects in struct page are organized in double word blocks in
  10.  * order to allows us to use atomic double word operations on portions
  11.  * of struct page. That is currently only used by slub but the arrangement
  12.  * allows the use of atomic double word operations on the flags/mapping
  13.  * and lru list pointers also.
  14.  */
  15. struct page {
  16.     /* First double word block */
  17.     unsigned long flags; /* Atomic flags, some possibly
  18.                      * updated asynchronously */
  19.     union {
  20.         struct address_space *mapping; /* If low bit clear, points to
  21.                          * inode address_space, or NULL.
  22.                          * If page mapped as anonymous
  23.                          * memory, low bit is set, and
  24.                          * it points to anon_vma object:
  25.                          * see PAGE_MAPPING_ANON below.
  26.                          */
  27.         void *s_mem; /* slab first object */
  28.     };
  29.  
  30.     /* Second double word */
  31.     struct {
  32.         union {
  33.             pgoff_t index; /* Our offset within mapping. */
  34.             void *freelist; /* sl[aou]b first free object */
  35.             bool pfmemalloc; /* If set by the page allocator,
  36.                          * ALLOC_NO_WATERMARKS was set
  37.                          * and the low watermark was not
  38.                          * met implying that the system
  39.                          * is under some pressure. The
  40.                          * caller should try ensure
  41.                          * this page is only used to
  42.                          * free other pages.
  43.                          */
  44.         };
  45.  
  46.         union {
  47. #if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
  48.     defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
  49.             /* Used for cmpxchg_double in slub */
  50.             unsigned long counters;
  51. #else
  52.             /*
  53.              * Keep _count separate from slub cmpxchg_double data.
  54.              * As the rest of the double word is protected by
  55.              * slab_lock but _count is not.
  56.              */
  57.             unsigned counters;
  58. #endif
  59.  
  60.             struct {
  61.  
  62.                 union {
  63.                     /*
  64.                      * Count of ptes mapped in
  65.                      * mms, to show when page is
  66.                      * mapped & limit reverse map
  67.                      * searches.
  68.                      *
  69.                      * Used also for tail pages
  70.                      * refcounting instead of
  71.                      * _count. Tail pages cannot
  72.                      * be mapped and keeping the
  73.                      * tail page _count zero at
  74.                      * all times guarantees
  75.                      * get_page_unless_zero() will
  76.                      * never succeed on tail
  77.                      * pages.
  78.                      */
  79.                     atomic_t _mapcount;
  80.  
  81.                     struct { /* SLUB */
  82.                         unsigned inuse:16;
  83.                         unsigned objects:15;
  84.                         unsigned frozen:1;
  85.                     };
  86.                     int units; /* SLOB */
  87.                 };
  88.                 atomic_t _count; /* Usage count, see below. */
  89.             };
  90.             unsigned int active; /* SLAB */
  91.         };
  92.     };
  93.  
  94.     /* Third double word block */
  95.     union {
  96.         struct list_head lru; /* Pageout list, eg. active_list
  97.                      * protected by zone->lru_lock !
  98.                      */
  99.         struct { /* slub per cpu partial pages */
  100.             struct page *next; /* Next partial slab */
  101. #ifdef CONFIG_64BIT
  102.             int pages; /* Nr of partial slabs left */
  103.             int pobjects; /* Approximate # of objects */
  104. #else
  105.             short int pages;
  106.             short int pobjects;
  107. #endif
  108.         };
  109.  
  110.         struct list_head list; /* slobs list of pages */
  111.         struct slab *slab_page; /* slab fields */
  112.         struct rcu_head rcu_head; /* Used by SLAB
  113.                          * when destroying via RCU
  114.                          */
  115. #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
  116.         pgtable_t pmd_huge_pte; /* protected by page->ptl */
  117. #endif
  118.     };
  119.  
  120.     /* Remainder is not double word aligned */
  121.     union {
  122.         unsigned long private; /* Mapping-private opaque data:
  123.                          * usually used for buffer_heads
  124.                          * if PagePrivate set; used for
  125.                          * swp_entry_t if PageSwapCache;
  126.                          * indicates order in the buddy
  127.                          * system if PG_buddy is set.
  128.                          */
  129. #if USE_SPLIT_PTE_PTLOCKS
  130. #if ALLOC_SPLIT_PTLOCKS
  131.         spinlock_t *ptl;
  132. #else
  133.         spinlock_t ptl;
  134. #endif
  135. #endif
  136.         struct kmem_cache *slab_cache; /* SL[AU]B: Pointer to slab */
  137.         struct page *first_page; /* Compound tail pages */
  138.     };
  139.  
  140.     /*
  141.      * On machines where all RAM is mapped into kernel address space,
  142.      * we can simply calculate the virtual address. On machines with
  143.      * highmem some memory is mapped into kernel virtual memory
  144.      * dynamically, so we need a place to store that address.
  145.      * Note that this field could be 16 bits on x86 ... ;)
  146.      *
  147.      * Architectures with slow multiplication can define
  148.      * WANT_PAGE_VIRTUAL in asm/page.h
  149.      */
  150. #if defined(WANT_PAGE_VIRTUAL)
  151.     void *virtual; /* Kernel virtual address (NULL if
  152.                        not kmapped, ie. highmem) */
  153. #endif /* WANT_PAGE_VIRTUAL */
  154. #ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
  155.     unsigned long debug_flags; /* Use atomic bitops on this */
  156. #endif
  157.  
  158. #ifdef CONFIG_KMEMCHECK
  159.     /*
  160.      * kmemcheck wants to track the status of each byte in a page; this
  161.      * is a pointer to such a status block. NULL if not tracked.
  162.      */
  163.     void *shadow;
  164. #endif
  165.  
  166. #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
  167.     int _last_cpupid;
  168. #endif
  169. }

(该结构很多union结构,主要是用于各种算法不同数据的空间复用,暂时记录部分常见的数据成员)

unsigned long flags;

——用于记录页框的类型;

struct address_space *mapping;

——用于区分该页是映射页框还是匿名页框;

atomic_t _mapcount;

——记录了系统中页表有多少项指向该页;

atomic_t _count;

——当前系统对该页面的引用次数;

struct list_head lru;

——当页框处于分配状态时,该成员用于zonelruvec里面的list,当页框未被分配时则用于伙伴算法;

unsigned long private;

——指向“私有”数据的指针。根据页的用途,可以用不同的方式使用该指针,通常用于与数据缓冲区关联起来;

void *virtual;

——用于高端内存区域的页,即用于无法直接映射的页,该成员用于存储该页的虚拟地址;

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