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内存管理篇-03物理内存管理-32位

news 来源：原创 2024/9/19 9:43:36

正片从现在开始了。

1.结构体关联

当DDR初始化后，整个内存就可以访问了。但是需要合理的管理，防止内存碎片以及安全相关的问题。因此需要对物理内存进行严格的管理。

物理内存分为：页，分区，内存节点。DMA需要连续的内存，因此需要单独的内存。（大概16MB）。

物理页帧结构体，每个物理块都通过一个struct page描述。

定义头文件：include/linux/mm_type.h 描述不同类型的页。
每个物理页帧page frame 都使用结构体page表示。
结构体struct page核心成员分析。
思考

- 物理页帧和struct page之间的关系：通过page结构体找到对应的页帧号。因为page结构体是线性存放。
- 不同类型的page分别有什么作用。
- 物理页帧号pfn 和物理地址的关系：通过页帧号找到对应的page结构体。
- struct page存储在哪里。page本身是需要占用内存的，每个页空间，都会用page结构体描述它。比如说系统总共有1024个page，那么就需要1024个page结构体来描述整个系统内存。此时需要类似struct page mm_map[1024]的信息来保存。
- 全局变量：mem_map。它保存了系统所有page的地址，因为系统所有的page都有对应的地址，需要这么一块内存指向它。

假设物理页帧号是0x10240000,0x10250000,0x10260000 ... 0x20470000, 如果用arr[1024]数组保存它,arr[0] = 0x10240000,arr[1] = 0x10250000, ... arr[1023] = 0x20470000。因此物理页帧号对应存放的地址：__page_to_pfn(page) ==> (page - mem_map)

示例1：如果已知page，要去求pfn

struct page my_page=mem_map[22]
my_page_pfn = (my_page - mem_map) + ARCH_PFN_OFFSET

示例2：如果已知某个pfn，去求page

my_pfn = 0x10250000
struct page my_page = mem_map + (pfn - ARCH_FPN_OFFSET)

2.内存页：page结构体

struct page 是 Linux 内核中的一个重要数据结构，用于表示和管理物理内存页。struct page 结构体的设计非常复杂，因为它必须能够适应多种不同的用途，包括但不限于页缓存、匿名页面、页表管理、内存池管理、内存控制组等。为了支持这些多样的用途，struct page 中包含了多个 union 联合体。

unsigned long flags 这个成员包含了一些标志位，用于表示页面的状态，如是否可写、是否脏、是否被锁定等。

struct page {unsigned long flags; /* 用于表示页面的状态，如是否可写、是否脏、是否被锁定等。/** Five words (20/40 bytes) are available in this union.* WARNING: bit 0 of the first word is used for PageTail(). That* means the other users of this union MUST NOT use the bit to* avoid collision and false-positive PageTail().*/union {struct {	/* Page cache and anonymous pages *//*** @lru: Pageout list, eg. active_list protected by* pgdat->lru_lock.  Sometimes used as a generic list* by the page owner.*/struct list_head lru;/* See page-flags.h for PAGE_MAPPING_FLAGS */struct address_space *mapping;pgoff_t index;		/* Our offset within mapping. *//*** @private: Mapping-private opaque data.* Usually used for buffer_heads if PagePrivate.* Used for swp_entry_t if PageSwapCache.* Indicates order in the buddy system if PageBuddy.*/unsigned long private;};struct {	/* page_pool used by netstack *//*** @dma_addr: might require a 64-bit value on* 32-bit architectures.*/unsigned long dma_addr[2];};struct {	/* slab, slob and slub */union {struct list_head slab_list;struct {	/* Partial pages */struct page *next;
#ifdef CONFIG_64BITint pages;	/* Nr of pages left */int pobjects;	/* Approximate count */
#elseshort int pages;short int pobjects;
#endif};};struct kmem_cache *slab_cache; /* not slob *//* Double-word boundary */void *freelist;		/* first free object */union {void *s_mem;	/* slab: first object */unsigned long counters;		/* SLUB */struct {			/* SLUB */unsigned inuse:16;unsigned objects:15;unsigned frozen:1;};};};struct {	/* Tail pages of compound page */unsigned long compound_head;	/* Bit zero is set *//* First tail page only */unsigned char compound_dtor;unsigned char compound_order;atomic_t compound_mapcount;unsigned int compound_nr; /* 1 << compound_order */};struct {	/* Second tail page of compound page */unsigned long _compound_pad_1;	/* compound_head */atomic_t hpage_pinned_refcount;/* For both global and memcg */struct list_head deferred_list;};struct {	/* Page table pages */unsigned long _pt_pad_1;	/* compound_head */pgtable_t pmd_huge_pte; /* protected by page->ptl */unsigned long _pt_pad_2;	/* mapping */union {struct mm_struct *pt_mm; /* x86 pgds only */atomic_t pt_frag_refcount; /* powerpc */};
#if ALLOC_SPLIT_PTLOCKSspinlock_t *ptl;
#elsespinlock_t ptl;
#endif};struct {	/* ZONE_DEVICE pages *//** @pgmap: Points to the hosting device page map. */struct dev_pagemap *pgmap;void *zone_device_data;/** ZONE_DEVICE private pages are counted as being* mapped so the next 3 words hold the mapping, index,* and private fields from the source anonymous or* page cache page while the page is migrated to device* private memory.* ZONE_DEVICE MEMORY_DEVICE_FS_DAX pages also* use the mapping, index, and private fields when* pmem backed DAX files are mapped.*/};/** @rcu_head: You can use this to free a page by RCU. */struct rcu_head rcu_head;};union {		/* This union is 4 bytes in size. *//** If the page can be mapped to userspace, encodes the number* of times this page is referenced by a page table.*/atomic_t _mapcount;/** If the page is neither PageSlab nor mappable to userspace,* the value stored here may help determine what this page* is used for.  See page-flags.h for a list of page types* which are currently stored here.*/unsigned int page_type;unsigned int active;		/* SLAB */int units;			/* SLOB */};/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */atomic_t _refcount;#ifdef CONFIG_MEMCGunion {struct mem_cgroup *mem_cgroup;struct obj_cgroup **obj_cgroups;};
#endif/** 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 ifnot kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGSint _last_cpupid;
#endif
} _struct_page_alignment;

3.内存区域：struct zone

定义：mmzone.h
重要结构体成员：_watermark watermark_boost zone_start_pfn present_pages free_area

- zone_start_pfn 起始页帧号 present_pages 该zone当前有多少个页
- lowmem_reseve备用内存，怎么理解？？

初始化：zone_sizes_init

zone_type

enum zone_type {
#ifdef CONFIG_ZONE_DMAZONE_DMA,
#endif
#ifdef CONFIG_ZONE_DMA32ZONE_DMA32,
#endifZONE_NORMAL,
#ifdef CONFIG_HIGHMEMZONE_HIGHMEM,
#endifZONE_MOVABLE,
#ifdef CONFIG_ZONE_DEVICEZONE_DEVICE,
#endif__MAX_NR_ZONES
};

struct zone

struct zone {/* Read-mostly fields *//* zone watermarks, access with *_wmark_pages(zone) macros */unsigned long _watermark[NR_WMARK]; 表示该内存区域的水印阈值，用于内存管理策略。unsigned long watermark_boost; 用于提高水印阈值的临时值。unsigned long nr_reserved_highatomic; 表示为高原子操作预留的页面数量。long lowmem_reserve[MAX_NR_ZONES]; 用于保留低内存区域的页面数量，以防上层内存充足而下层内存不足的情况。
#ifdef CONFIG_NEED_MULTIPLE_NODESint node; 表示该内存区域所在的 NUMA 节点编号。
#endifstruct pglist_data	*zone_pgdat; 用于描述整个内存区域的元数据。struct per_cpu_pageset __percpu *pageset;#ifndef CONFIG_SPARSEMEMunsigned long		*pageblock_flags; 用于标记页面块的标志，例如页面是否可移动等。
#endif /* CONFIG_SPARSEMEM *//* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */unsigned long		zone_start_pfn; 示该内存区域起始的物理页号。atomic_long_t		managed_pages; 表示该内存区域中由 buddy 系统管理的页面数量。unsigned long		spanned_pages; 表示该内存区域覆盖的总页数，包括空洞区域。unsigned long		present_pages; 表示该内存区域存在的物理页数，不包括空洞区域。const char		*name;#ifdef CONFIG_MEMORY_ISOLATIONunsigned long		nr_isolate_pageblock;
#endif#ifdef CONFIG_MEMORY_HOTPLUG/* see spanned/present_pages for more description */seqlock_t		span_seqlock;
#endifint initialized; 表示该内存区域是否已经初始化。/* Write-intensive fields used from the page allocator */ZONE_PADDING(_pad1_)/* free areas of different sizes */struct free_area	free_area[MAX_ORDER]; 用于表示不同大小的空闲页面区域。/* zone flags, see below */unsigned long		flags; 包含该内存区域的标志位，如是否支持 NUMA 等/* Primarily protects free_area */spinlock_t		lock;/* Write-intensive fields used by compaction and vmstats. */ZONE_PADDING(_pad2_)/** 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 compaction migration scanner should start */unsigned long		compact_cached_migrate_pfn[ASYNC_AND_SYNC];unsigned long		compact_init_migrate_pfn;unsigned long		compact_init_free_pfn;
#endif#ifdef CONFIG_COMPACTIONunsigned int		compact_considered;unsigned int		compact_defer_shift;int			compact_order_failed;
#endif#if defined CONFIG_COMPACTION || defined CONFIG_CMA/* Set to true when the PG_migrate_skip bits should be cleared */bool			compact_blockskip_flush; 表示是否应清除 PG_migrate_skip 标志。
#endifbool			contiguous; 表示该内存区域是否支持连续内存分配。ZONE_PADDING(_pad3_)/* Zone statistics */atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS]; 维护关于该内存区域的各种统计信息。atomic_long_t		vm_numa_stat[NR_VM_NUMA_STAT_ITEMS]; 维护关于该内存区域的 NUMA 相关统计信息。
} ____cacheline_internodealigned_in_smp;