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。
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【file:/include/linux/mmzone.h】
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typedef struct pglist_data {
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struct zone node_zones[MAX_NR_ZONES];
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struct zonelist node_zonelists[MAX_ZONELISTS];
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int nr_zones;
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#ifdef CONFIG_FLAT_NODE_MEM_MAP /* means !SPARSEMEM */
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struct page *node_mem_map;
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#ifdef CONFIG_MEMCG
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struct page_cgroup *node_page_cgroup;
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#endif
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#endif
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#ifndef CONFIG_NO_BOOTMEM
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struct bootmem_data *bdata;
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#endif
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#ifdef CONFIG_MEMORY_HOTPLUG
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/*
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* Must be held any time you expect node_start_pfn, node_present_pages
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* or node_spanned_pages stay constant. Holding this will also
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* guarantee that any pfn_valid() stays that way.
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*
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* pgdat_resize_lock() and pgdat_resize_unlock() are provided to
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* manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG.
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*
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* Nests above zone->lock and zone->span_seqlock
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*/
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spinlock_t node_size_lock;
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#endif
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unsigned long node_start_pfn;
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unsigned long node_present_pages; /* total number of physical pages */
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unsigned long node_spanned_pages; /* total size of physical page
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range, including holes */
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int node_id;
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nodemask_t reclaim_nodes; /* Nodes allowed to reclaim from */
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wait_queue_head_t kswapd_wait;
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wait_queue_head_t pfmemalloc_wait;
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struct task_struct *kswapd; /* Protected by lock_memory_hotplug() */
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int kswapd_max_order;
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enum zone_type classzone_idx;
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#ifdef CONFIG_NUMA_BALANCING
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/* Lock serializing the migrate rate limiting window */
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spinlock_t numabalancing_migrate_lock;
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/* Rate limiting time interval */
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unsigned long numabalancing_migrate_next_window;
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/* Number of pages migrated during the rate limiting time interval */
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unsigned long numabalancing_migrate_nr_pages;
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#endif
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} 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_cgroup是page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;
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【file:/include/linux/mmzone.h】
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struct zone {
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/* Fields commonly accessed by the page allocator */
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/* zone watermarks, access with *_wmark_pages(zone) macros */
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unsigned long watermark[NR_WMARK];
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/*
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* When free pages are below this point, additional steps are taken
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* when reading the number of free pages to avoid per-cpu counter
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* drift allowing watermarks to be breached
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*/
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unsigned long percpu_drift_mark;
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/*
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* We don't know if the memory that we're going to allocate will be freeable
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* or/and it will be released eventually, so to avoid totally wasting several
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* GB of ram we must reserve some of the lower zone memory (otherwise we risk
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* to run OOM on the lower zones despite there's tons of freeable ram
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* on the higher zones). This array is recalculated at runtime if the
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* sysctl_lowmem_reserve_ratio sysctl changes.
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*/
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unsigned long lowmem_reserve[MAX_NR_ZONES];
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/*
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* This is a per-zone reserve of pages that should not be
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* considered dirtyable memory.
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*/
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unsigned long dirty_balance_reserve;
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#ifdef CONFIG_NUMA
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int node;
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/*
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* zone reclaim becomes active if more unmapped pages exist.
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*/
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unsigned long min_unmapped_pages;
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unsigned long min_slab_pages;
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#endif
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struct per_cpu_pageset __percpu *pageset;
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/*
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* free areas of different sizes
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*/
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spinlock_t lock;
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#if defined CONFIG_COMPACTION || defined CONFIG_CMA
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/* Set to true when the PG_migrate_skip bits should be cleared */
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bool compact_blockskip_flush;
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/* pfns where compaction scanners should start */
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unsigned long compact_cached_free_pfn;
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unsigned long compact_cached_migrate_pfn;
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#endif
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#ifdef CONFIG_MEMORY_HOTPLUG
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/* see spanned/present_pages for more description */
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seqlock_t span_seqlock;
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#endif
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struct free_area free_area[MAX_ORDER];
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#ifndef CONFIG_SPARSEMEM
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/*
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* Flags for a pageblock_nr_pages block. See pageblock-flags.h.
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* In SPARSEMEM, this map is stored in struct mem_section
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*/
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unsigned long *pageblock_flags;
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#endif /* CONFIG_SPARSEMEM */
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#ifdef CONFIG_COMPACTION
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/*
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* On compaction failure, 1<<compact_defer_shift compactions
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* are skipped before trying again. The number attempted since
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* last failure is tracked with compact_considered.
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*/
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unsigned int compact_considered;
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unsigned int compact_defer_shift;
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int compact_order_failed;
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#endif
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ZONE_PADDING(_pad1_)
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/* Fields commonly accessed by the page reclaim scanner */
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spinlock_t lru_lock;
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struct lruvec lruvec;
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unsigned long pages_scanned; /* since last reclaim */
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unsigned long flags; /* zone flags, see below */
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/* Zone statistics */
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atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
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/*
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* The target ratio of ACTIVE_ANON to INACTIVE_ANON pages on
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* this zone's LRU. Maintained by the pageout code.
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*/
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unsigned int inactive_ratio;
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ZONE_PADDING(_pad2_)
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/* Rarely used or read-mostly fields */
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/*
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* wait_table -- the array holding the hash table
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* wait_table_hash_nr_entries -- the size of the hash table array
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* wait_table_bits -- wait_table_size == (1 << wait_table_bits)
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*
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* The purpose of all these is to keep track of the people
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* waiting for a page to become available and make them
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* runnable again when possible. The trouble is that this
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* consumes a lot of space, especially when so few things
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* wait on pages at a given time. So instead of using
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* per-page waitqueues, we use a waitqueue hash table.
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*
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* The bucket discipline is to sleep on the same queue when
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* colliding and wake all in that wait queue when removing.
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* When something wakes, it must check to be sure its page is
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* truly available, a la thundering herd. The cost of a
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* collision is great, but given the expected load of the
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* table, they should be so rare as to be outweighed by the
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* benefits from the saved space.
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*
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* __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the
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* primary users of these fields, and in mm/page_alloc.c
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* free_area_init_core() performs the initialization of them.
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*/
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wait_queue_head_t * wait_table;
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unsigned long wait_table_hash_nr_entries;
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unsigned long wait_table_bits;
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/*
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* Discontig memory support fields.
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*/
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struct pglist_data *zone_pgdat;
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/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
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unsigned long zone_start_pfn;
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/*
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* spanned_pages is the total pages spanned by the zone, including
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* holes, which is calculated as:
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* spanned_pages = zone_end_pfn - zone_start_pfn;
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*
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* present_pages is physical pages existing within the zone, which
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* is calculated as:
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* present_pages = spanned_pages - absent_pages(pages in holes);
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*
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* managed_pages is present pages managed by the buddy system, which
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* is calculated as (reserved_pages includes pages allocated by the
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* bootmem allocator):
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* managed_pages = present_pages - reserved_pages;
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*
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* So present_pages may be used by memory hotplug or memory power
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* management logic to figure out unmanaged pages by checking
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* (present_pages - managed_pages). And managed_pages should be used
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* by page allocator and vm scanner to calculate all kinds of watermarks
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* and thresholds.
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*
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* Locking rules:
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*
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* zone_start_pfn and spanned_pages are protected by span_seqlock.
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* It is a seqlock because it has to be read outside of zone->lock,
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* and it is done in the main allocator path. But, it is written
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* quite infrequently.
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*
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* The span_seq lock is declared along with zone->lock because it is
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* frequently read in proximity to zone->lock. It's good to
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* give them a chance of being in the same cacheline.
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*
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* Write access to present_pages at runtime should be protected by
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* lock_memory_hotplug()/unlock_memory_hotplug(). Any reader who can't
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* tolerant drift of present_pages should hold memory hotplug lock to
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* get a stable value.
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*
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* Read access to managed_pages should be safe because it's unsigned
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* long. Write access to zone->managed_pages and totalram_pages are
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* protected by managed_page_count_lock at runtime. Idealy only
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* adjust_managed_page_count() should be used instead of directly
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* touching zone->managed_pages and totalram_pages.
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*/
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unsigned long spanned_pages;
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unsigned long present_pages;
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unsigned long managed_pages;
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/*
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* Number of MIGRATE_RESEVE page block. To maintain for just
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* optimization. Protected by zone->lock.
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*/
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int nr_migrate_reserve_block;
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/*
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* rarely used fields:
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*/
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const char *name;
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} ____cacheline_internodealigned_in_smp;
unsigned
long watermark[NR_WMARK];
——该数组有三个值WMARK_MIN、WMARK_LOW、WMARK_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;
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【file:/include/linux/mmzone.h】
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/*
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* Each physical page in the system has a struct page associated with
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* it to keep track of whatever it is we are using the page for at the
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* moment. Note that we have no way to track which tasks are using
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* a page, though if it is a pagecache page, rmap structures can tell us
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* who is mapping it.
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*
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* The objects in struct page are organized in double word blocks in
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* order to allows us to use atomic double word operations on portions
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* of struct page. That is currently only used by slub but the arrangement
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* allows the use of atomic double word operations on the flags/mapping
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* and lru list pointers also.
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*/
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struct page {
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/* First double word block */
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unsigned long flags; /* Atomic flags, some possibly
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* updated asynchronously */
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union {
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struct address_space *mapping; /* If low bit clear, points to
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* inode address_space, or NULL.
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* If page mapped as anonymous
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* memory, low bit is set, and
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* it points to anon_vma object:
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* see PAGE_MAPPING_ANON below.
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*/
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void *s_mem; /* slab first object */
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};
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/* Second double word */
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struct {
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union {
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pgoff_t index; /* Our offset within mapping. */
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void *freelist; /* sl[aou]b first free object */
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bool pfmemalloc; /* If set by the page allocator,
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* ALLOC_NO_WATERMARKS was set
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* and the low watermark was not
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* met implying that the system
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* is under some pressure. The
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* caller should try ensure
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* this page is only used to
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* free other pages.
-
*/
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};
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-
union {
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#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
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defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
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/* Used for cmpxchg_double in slub */
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unsigned long counters;
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#else
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/*
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* Keep _count separate from slub cmpxchg_double data.
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* As the rest of the double word is protected by
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* slab_lock but _count is not.
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*/
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unsigned counters;
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#endif
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-
struct {
-
-
union {
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/*
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* Count of ptes mapped in
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* mms, to show when page is
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* mapped & limit reverse map
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* searches.
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*
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* Used also for tail pages
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* refcounting instead of
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* _count. Tail pages cannot
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* be mapped and keeping the
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* tail page _count zero at
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* all times guarantees
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* get_page_unless_zero() will
-
* never succeed on tail
-
* pages.
-
*/
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atomic_t _mapcount;
-
-
struct { /* SLUB */
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unsigned inuse:16;
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unsigned objects:15;
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unsigned frozen:1;
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};
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int units; /* SLOB */
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};
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atomic_t _count; /* Usage count, see below. */
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};
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unsigned int active; /* SLAB */
-
};
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};
-
-
/* Third double word block */
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union {
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struct list_head lru; /* Pageout list, eg. active_list
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* protected by zone->lru_lock !
-
*/
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struct { /* slub per cpu partial pages */
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struct page *next; /* Next partial slab */
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#ifdef CONFIG_64BIT
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int pages; /* Nr of partial slabs left */
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int pobjects; /* Approximate # of objects */
-
#else
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short int pages;
-
short int pobjects;
-
#endif
-
};
-
-
struct list_head list; /* slobs list of pages */
-
struct slab *slab_page; /* slab fields */
-
struct rcu_head rcu_head; /* Used by SLAB
-
* when destroying via RCU
-
*/
-
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
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pgtable_t pmd_huge_pte; /* protected by page->ptl */
-
#endif
-
};
-
-
/* Remainder is not double word aligned */
-
union {
-
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.
-
*/
-
#if USE_SPLIT_PTE_PTLOCKS
-
#if ALLOC_SPLIT_PTLOCKS
-
spinlock_t *ptl;
-
#else
-
spinlock_t ptl;
-
#endif
-
#endif
-
struct kmem_cache *slab_cache; /* SL[AU]B: Pointer to slab */
-
struct page *first_page; /* Compound tail pages */
-
};
-
-
/*
-
* 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
-
-
#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
-
int _last_cpupid;
-
#endif
-
}
(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zone的lruvec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;