Linux内核之物理内存组织结构
一、系统调用mmap
虚拟内存区域使用起始地址和结束地址描述，链表按起始地址递增排序。两系统调用区别：mmap指定的偏移的单位是字节，而mmap2指定的偏移的单位是页。arm64架构实现系统调用mmap。
二、系统调用munmap
系统调用munmap用来删除内存映射，它有两个参数：起始地址和长度即可。它的主要工作委托给内核源码文件处理“mm/mmap.c”中的函数do_munmap。
vm_munmap-->do_munmap -->vma = find_vma(mm,start) -->error = __split_vma(mm,vma,start,0) -->last = find_vma(mm,end) -->int error = __split_vma(mm,last,end,1) -->munlock_vma_pages_all -->detach_vmas_to_be_unmapped -->unmap_region -->arch_unmap -->remove_vma_list
vma = find_vma(mm,start);//根据起始地址找到要删除的第一个虚拟内存区域vma
error = __split_vma(mm,vma,start,0);//如果只删除虚拟内存区域vma的部分，那么分裂虚拟内存区域vma
last = find_vma(mm,end);//根据结束地址找到要删除的最后一个虚拟内存区域vma
int error = __split_vma(mm,last,end,1);//如果只删除虚拟内存区域last的一部分，那么分裂虚拟内存区域vma
munlock_vma_pages_all;//针对所有删除目标，如果虚拟内存区域被锁定在内存中（不允许换出到交换区），调用函数解除锁定
detach_vmas_to_be_unmapped;//调用此函数，把所有删除目标从进程虚拟内存区域链表和树中删除，单独组成一条临时链表
unmap_region;//调用此函数，针对所有删除目标，在进程的页表中删除映射，并且从处理器的页表缓存中删除映射
arch_unmap;//调用此函数执行处理器架构特定的处理操作
remove_vma_list;//调用此函数，删除所有目标
三、物理内存组织结构
1.体系结构
目前多处理器系统有两种体系结构：
非一致内存访问（non-unit memory access，numa）：指内存被划分成多个内存节点的多处理器系统。访问一个内存节点花费的时间取决于处理器和内存节点的距离。
对称多处理器（sysmmetric muti-processor，smp）：即一致内存访问（uniform memory access，uma），所有处理器访问内存花费的时间是相同的。
2.内存模型
内存模型是从处理器角度看到的物理内存分布，内核管理不同内存模型的方式存在差异。内存管理子系统支持3种内存模型：
平坦内存（flat memory）：内存的物理地址空间是连续的，没有空洞。
不连续内存（discontiguous memory）：内存的物理地址空间存在空洞，这种模型可以高效地处理空洞。
稀疏内存（space memory）：内存物理地址空间存在空洞，如果要支持内存热插拔，只能选择稀疏内存模型。
3.三级结构
内存管理子系统使用节点（node）、区域（zone）、页（page）三级结构描述物理内存。
3.1 内存节点--->分为两种情况
numa体系的内存节点，根据处理器和内存距离划分；
在具有不连续内存的numa系统中，表示比区域的级别更高的内存区域，根据物理地址是否连续，每块物理地址连续的内存是一个内存节点。
内存节点使用结构体pglist_data描述内存布局
linux内核源码如下：
typedef struct pglist_data { struct zone node_zones[max_nr_zones]; // 内存区域数组 struct zonelist node_zonelists[max_zonelists]; // 备用区域列表 int nr_zones; // 该节点包含内存区域数量#ifdef config_flat_node_mem_map /* means !sparsemem */ // 除了稀疏内存模型以外 struct page *node_mem_map; // 页描述符数组#ifdef config_page_extension struct page_ext *node_page_ext; // 页的扩展属性#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; // 该节点的起始物理页号 unsigned long node_present_pages; /* 物理页总数 */ unsigned long node_spanned_pages; /* 物理页范围总的长度，包括空间*/ int node_id; // 节点标识符 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;#endif /* config_deferred_struct_page_init */} pg_data_t;
node_mem_map此成员指向页描述符数组，每个物理页对应一个页描述符。
node是内存管理最顶层的结构，在numa架构下，cpu平均划分为多个node，每个node有自己的内存控制器及内存插槽。cpu访问自己node上内存速度快，而访问其他cpu所关联node的内存速度慢。uma被当作只一个node的numa系统。
3.2 内存区域（zone）
内存节点被划分为内存区域。linux内核源码分析：include/linux/mmzone.h
enum zone_type {#ifdef config_zone_dma /* * zone_dma is used when there are devices that are not able * to do dma to all of addressable memory (zone_normal). then we * carve out the portion of memory that is needed for these devices. * the range is arch specific. * * some examples * * architecture limit * --------------------------- * parisc, ia64, sparc <4g * s390 <2g * arm various * alpha unlimited or 0-16mb. * * i386, x86_64 and multiple other arches * > page_shift */ unsigned long zone_start_pfn; // 当前区域的起始物理页号 /* * 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); * * 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; * * 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. * * read access to managed_pages should be safe because it's unsigned * long. write access to zone->managed_pages and totalram_pages are * protected by managed_page_count_lock at runtime. idealy only * adjust_managed_page_count() should be used instead of directly * touching zone->managed_pages and totalram_pages. */ unsigned long managed_pages; // 伙伴分配器管理的物理页的数量 unsigned long spanned_pages; // 当前区域跨越的总页数，包括空洞 unsigned long present_pages; // 当前区域存在的物理页的数量，不包括空洞 const char *name; // 区域名称#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 /* * wait_table -- the array holding the hash table * wait_table_hash_nr_entries -- the size of the hash table array * wait_table_bits -- wait_table_size == (1 << wait_table_bits) * * the purpose of all these is to keep track of the people * waiting for a page to become available and make them * runnable again when possible. the trouble is that this * consumes a lot of space, especially when so few things * wait on pages at a given time. so instead of using * per-page waitqueues, we use a waitqueue hash table. * * the bucket discipline is to sleep on the same queue when * colliding and wake all in that wait queue when removing. * when something wakes, it must check to be sure its page is * truly available, a la thundering herd. the cost of a * collision is great, but given the expected load of the * table, they should be so rare as to be outweighed by the * benefits from the saved space. * * __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the * primary users of these fields, and in mm/page_alloc.c * free_area_init_core() performs the initialization of them. */ wait_queue_head_t *wait_table; unsigned long wait_table_hash_nr_entries; unsigned long wait_table_bits; zone_padding(_pad1_) /* free areas of different sizes */ struct free_area free_area[max_order]; // 不同长度的空间区域 /* zone flags, see below */ unsigned long flags; /* write-intensive fields used from the page allocator */ spinlock_t lock; zone_padding(_pad2_) /* write-intensive fields used by page reclaim */ /* fields commonly accessed by the page reclaim scanner */ spinlock_t lru_lock; struct lruvec lruvec; /* evictions & activations on the inactive file list */ atomic_long_t inactive_age; /* * 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 async and sync compaction migration scanner should start */ unsigned long compact_cached_migrate_pfn[2];#endif#ifdef config_compaction /* * on compaction failure, 1< 3.3 物理页
页是内存管理当中最小单位，页面中的内存其物理地址是连续的，每个物理页由struct page描述。为了节省内存，struct page是个联合体。
页，又称为页帧，在内核当中，内存管理单元mmu（负责虚拟地址和物理地址转换的硬件）是把物理页page作为内存管理的基本单位。体系结构不同，支持的页大小也不同。（32位体系结构支持4kb的页、64位体系结构支持8kb的页、mips64架构体系支持16kb的页）
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Linux内核之物理内存组织结构
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虚拟内存区域使用起始地址和结束地址描述，链表按起始地址递增排序。两系统调用区别：mmap指定的偏移的单位是字节，而mmap2指定的偏移的单位是页。arm64架构实现系统调用mmap。
二、系统调用munmap
系统调用munmap用来删除内存映射，它有两个参数：起始地址和长度即可。它的主要工作委托给内核源码文件处理“mm/mmap.c”中的函数do_munmap。
vm_munmap-->do_munmap -->vma = find_vma(mm,start) -->error = __split_vma(mm,vma,start,0) -->last = find_vma(mm,end) -->int error = __split_vma(mm,last,end,1) -->munlock_vma_pages_all -->detach_vmas_to_be_unmapped -->unmap_region -->arch_unmap -->remove_vma_list
vma = find_vma(mm,start);//根据起始地址找到要删除的第一个虚拟内存区域vma
error = __split_vma(mm,vma,start,0);//如果只删除虚拟内存区域vma的部分，那么分裂虚拟内存区域vma
last = find_vma(mm,end);//根据结束地址找到要删除的最后一个虚拟内存区域vma
int error = __split_vma(mm,last,end,1);//如果只删除虚拟内存区域last的一部分，那么分裂虚拟内存区域vma
munlock_vma_pages_all;//针对所有删除目标，如果虚拟内存区域被锁定在内存中（不允许换出到交换区），调用函数解除锁定
detach_vmas_to_be_unmapped;//调用此函数，把所有删除目标从进程虚拟内存区域链表和树中删除，单独组成一条临时链表
unmap_region;//调用此函数，针对所有删除目标，在进程的页表中删除映射，并且从处理器的页表缓存中删除映射
arch_unmap;//调用此函数执行处理器架构特定的处理操作
remove_vma_list;//调用此函数，删除所有目标
三、物理内存组织结构
1.体系结构
目前多处理器系统有两种体系结构：
非一致内存访问（non-unit memory access，numa）：指内存被划分成多个内存节点的多处理器系统。访问一个内存节点花费的时间取决于处理器和内存节点的距离。
对称多处理器（sysmmetric muti-processor，smp）：即一致内存访问（uniform memory access，uma），所有处理器访问内存花费的时间是相同的。
2.内存模型
内存模型是从处理器角度看到的物理内存分布，内核管理不同内存模型的方式存在差异。内存管理子系统支持3种内存模型：
平坦内存（flat memory）：内存的物理地址空间是连续的，没有空洞。
不连续内存（discontiguous memory）：内存的物理地址空间存在空洞，这种模型可以高效地处理空洞。
稀疏内存（space memory）：内存物理地址空间存在空洞，如果要支持内存热插拔，只能选择稀疏内存模型。
3.三级结构
内存管理子系统使用节点（node）、区域（zone）、页（page）三级结构描述物理内存。
3.1 内存节点--->分为两种情况
numa体系的内存节点，根据处理器和内存距离划分；
在具有不连续内存的numa系统中，表示比区域的级别更高的内存区域，根据物理地址是否连续，每块物理地址连续的内存是一个内存节点。
内存节点使用结构体pglist_data描述内存布局
linux内核源码如下：
typedef struct pglist_data { struct zone node_zones[max_nr_zones]; // 内存区域数组 struct zonelist node_zonelists[max_zonelists]; // 备用区域列表 int nr_zones; // 该节点包含内存区域数量#ifdef config_flat_node_mem_map /* means !sparsemem */ // 除了稀疏内存模型以外 struct page *node_mem_map; // 页描述符数组#ifdef config_page_extension struct page_ext *node_page_ext; // 页的扩展属性#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; // 该节点的起始物理页号 unsigned long node_present_pages; /* 物理页总数 */ unsigned long node_spanned_pages; /* 物理页范围总的长度，包括空间*/ int node_id; // 节点标识符 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;#endif /* config_deferred_struct_page_init */} pg_data_t;
node_mem_map此成员指向页描述符数组，每个物理页对应一个页描述符。
node是内存管理最顶层的结构，在numa架构下，cpu平均划分为多个node，每个node有自己的内存控制器及内存插槽。cpu访问自己node上内存速度快，而访问其他cpu所关联node的内存速度慢。uma被当作只一个node的numa系统。
3.2 内存区域（zone）
内存节点被划分为内存区域。linux内核源码分析：include/linux/mmzone.h
enum zone_type {#ifdef config_zone_dma /* * zone_dma is used when there are devices that are not able * to do dma to all of addressable memory (zone_normal). then we * carve out the portion of memory that is needed for these devices. * the range is arch specific. * * some examples * * architecture limit * --------------------------- * parisc, ia64, sparc <4g * s390 <2g * arm various * alpha unlimited or 0-16mb. * * i386, x86_64 and multiple other arches * > page_shift */ unsigned long zone_start_pfn; // 当前区域的起始物理页号 /* * 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); * * 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; * * 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. * * read access to managed_pages should be safe because it's unsigned * long. write access to zone->managed_pages and totalram_pages are * protected by managed_page_count_lock at runtime. idealy only * adjust_managed_page_count() should be used instead of directly * touching zone->managed_pages and totalram_pages. */ unsigned long managed_pages; // 伙伴分配器管理的物理页的数量 unsigned long spanned_pages; // 当前区域跨越的总页数，包括空洞 unsigned long present_pages; // 当前区域存在的物理页的数量，不包括空洞 const char *name; // 区域名称#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 /* * wait_table -- the array holding the hash table * wait_table_hash_nr_entries -- the size of the hash table array * wait_table_bits -- wait_table_size == (1 << wait_table_bits) * * the purpose of all these is to keep track of the people * waiting for a page to become available and make them * runnable again when possible. the trouble is that this * consumes a lot of space, especially when so few things * wait on pages at a given time. so instead of using * per-page waitqueues, we use a waitqueue hash table. * * the bucket discipline is to sleep on the same queue when * colliding and wake all in that wait queue when removing. * when something wakes, it must check to be sure its page is * truly available, a la thundering herd. the cost of a * collision is great, but given the expected load of the * table, they should be so rare as to be outweighed by the * benefits from the saved space. * * __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the * primary users of these fields, and in mm/page_alloc.c * free_area_init_core() performs the initialization of them. */ wait_queue_head_t *wait_table; unsigned long wait_table_hash_nr_entries; unsigned long wait_table_bits; zone_padding(_pad1_) /* free areas of different sizes */ struct free_area free_area[max_order]; // 不同长度的空间区域 /* zone flags, see below */ unsigned long flags; /* write-intensive fields used from the page allocator */ spinlock_t lock; zone_padding(_pad2_) /* write-intensive fields used by page reclaim */ /* fields commonly accessed by the page reclaim scanner */ spinlock_t lru_lock; struct lruvec lruvec; /* evictions & activations on the inactive file list */ atomic_long_t inactive_age; /* * 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 async and sync compaction migration scanner should start */ unsigned long compact_cached_migrate_pfn[2];#endif#ifdef config_compaction /* * on compaction failure, 1<
页是内存管理当中最小单位，页面中的内存其物理地址是连续的，每个物理页由struct page描述。为了节省内存，struct page是个联合体。
页，又称为页帧，在内核当中，内存管理单元mmu（负责虚拟地址和物理地址转换的硬件）是把物理页page作为内存管理的基本单位。体系结构不同，支持的页大小也不同。（32位体系结构支持4kb的页、64位体系结构支持8kb的页、mips64架构体系支持16kb的页）
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