專題：Linux內存管理專題
關鍵詞：用戶內核空間划分、Node/Zone/Page、memblock、PGD/PUD/PMD/PTE、lowmem/highmem、ZONE_DMA/ZONE_NORMAL/ZONE_HIGHMEM、Watermark、MIGRATE_TYPES。
物理內存初始化是隨着Linux內核初始化進行的，同時內存管理也是其他很多其他功能的基礎。和內核中各種模塊耦合在一起。
在進行初始化之前，了解Linux內存管理框架圖有助於對內存管理有個大概的映像。
首先，需要知道整個用戶和內核空間是如何划分的(3:1、2:2)，然后從Node->Zone->Page的層級進行初始化，直到內存達到可用狀態。
關於Nodes、Zones、Pages三者之間的關系，《ULVMM》 Figure 2.1介紹，雖然zone_mem_map一層已經被替代，但是仍然反映了他們之間的層級樹形關系。
pg_data_t對應一個Node，node_zones包含了不同Zone；Zone下又定義了per_cpu_pageset，將page和cpu綁定。
start_kernel-->
page_address_init
setup_arch-->setup_machine_fdt-->early_init_dt_scan_nodes-->early_init_dt_scan_memory-->early_init_dt_add_memory_arch-->memblock_add
init_mm
early_paging_init
setup_dma_zone
sanity_check_meminfo
arm_memblock_init
paging_init
mm_init_cpumask
build_all_zonelists-------------------------
page_alloc_init
vfs_caches_init_early
mm_init
kmem_cache_init_late
debug_objects_mem_init
kmemleak_init
setup_per_cpu_pageset
numa_policy_init
anon_vma_init
page_writeback_init
1. 用戶空間和內核空間划分
32位Linux中，虛擬地址空間共4GB。將整個虛擬地址空間划分為用戶空間+內核空間，有三種：
choice prompt "Memory split" depends on MMU default VMSPLIT_3G help Select the desired split between kernel and user memory. If you are not absolutely sure what you are doing, leave this option alone! config VMSPLIT_3G bool "3G/1G user/kernel split" config VMSPLIT_2G bool "2G/2G user/kernel split" config VMSPLIT_1G bool "1G/3G user/kernel split" endchoice config PAGE_OFFSET hex default PHYS_OFFSET if !MMU default 0x40000000 if VMSPLIT_1G default 0x80000000 if VMSPLIT_2G default 0xC0000000
這樣配置的結果就是生成的autoconf.h定義了#define CONFIG_PAGE_OFFSET 0xC0000000。
在arch/arm/include/asm/memory.h中，可以看出PAGE_OFFSET是用戶空間和內核空間的分水嶺。也是用內核空間的起始點。
/* PAGE_OFFSET - the virtual address of the start of the kernel image */ #define PAGE_OFFSET UL(CONFIG_PAGE_OFFSET) static inline phys_addr_t __virt_to_phys(unsigned long x) { return (phys_addr_t)x - PAGE_OFFSET + PHYS_OFFSET; } static inline unsigned long __phys_to_virt(phys_addr_t x) { return x - PHYS_OFFSET + PAGE_OFFSET; }
2. 獲取物理內存大小
后面的一切初始化以及內存管理都是基於物理內存，所以首先要獲取物理內存的物理地址和大小。
通過DTS獲取物理內存屬性，然后解析並添加到memblock子系統中。
arch/arm/boot/dts/vexpress-v2p-ca9.dts： memory@60000000 { device_type = "memory"; reg = <0x60000000 0x40000000>; };
根據上面的dts，在start_kernel-->setup_arch-->setup_machine_fdt-->early_init_dt_scan_nodes-->of_scan_flat_dt(遍歷Nodes)-->early_init_dt_scan_memory(初始化單個內存Node)。
結果是從DTS解析出base size分別是0x60000000 0x40000000。
int __init early_init_dt_scan_memory(unsigned long node, const char *uname, int depth, void *data) { const char *type = of_get_flat_dt_prop(node, "device_type", NULL);----------------------------------device_type = "memory" ... reg = of_get_flat_dt_prop(node, "linux,usable-memory", &l); if (reg == NULL) reg = of_get_flat_dt_prop(node, "reg", &l);---------------------------------------------------reg = <0x60000000 0x40000000> if (reg == NULL) return 0; endp = reg + (l / sizeof(__be32)); pr_debug("memory scan node %s, reg size %d, data: %x %x %x %x,\n", uname, l, reg[0], reg[1], reg[2], reg[3]); while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) { u64 base, size; base = dt_mem_next_cell(dt_root_addr_cells, ®);--------------------------------------------0x60000000 size = dt_mem_next_cell(dt_root_size_cells, ®);--------------------------------------------0x40000000 ... early_init_dt_add_memory_arch(base, size);----------------------------------------------------進行base, size有效性檢查 } return 0; }
然后根據解析出的base/size，調用early_init_dt_add_memory_arch-->memblock_add-->memblock_add_range將解析出的物理內存加入到memblock子系統中。
struct memblock { bool bottom_up; /* is bottom up direction? */ phys_addr_t current_limit; struct memblock_type memory;-------------------添加物理內存區域 struct memblock_type reserved;-----------------添加預留內存區域 #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP struct memblock_type physmem; #endif };
memblock_add用於添加region到memblock.memory中；在內核初始化階段很多地方(比如哈arm_memblock_init)使用memblock_reserve將region添加到memblock.reserved。
memblock_remove用於將一個region從memblock.memory中移除，memblock_free等用於將一個region從memblock.reserved中移除。
這里面的地址都是物理地址，所有的信息都在memblock這個全局變量中。
int __init_memblock memblock_add_range(struct memblock_type *type, phys_addr_t base, phys_addr_t size, int nid, unsigned long flags) { bool insert = false; phys_addr_t obase = base; phys_addr_t end = base + memblock_cap_size(base, &size); int i, nr_new; if (!size) return 0; /* special case for empty array */ if (type->regions[0].size == 0) { WARN_ON(type->cnt != 1 || type->total_size); type->regions[0].base = base; type->regions[0].size = size; type->regions[0].flags = flags; memblock_set_region_node(&type->regions[0], nid); type->total_size = size; return 0; } repeat: /* * The following is executed twice. Once with %false @insert and * then with %true. The first counts the number of regions needed * to accomodate the new area. The second actually inserts them. */ ... }
memblock
在內核啟動階段，也有內存管理的需求，但是此時伙伴系統並沒有完成初始化。在早期內核中使用bootmem機制，作為內核初始化階段的內存分配器。
后來使用memblock作為內核初始化階段內存分配器，用於內存分配和釋放。
CONFIG_NO_BOOTMEM用於決定是否使用bootmem，Vexpress使能，所以使用memblock作為初始化階段的內存分配器。
因為bootmem和memblock兩者API兼容，所以使用者無感。使用memblock的時候編譯mm/nobootmem.c，調用memblock.c中的分配器接口。
3. 物理內存映射
由於沒有打開CONFIG_ARM_LPAE，Linux頁表采用兩層映射。所以PGD->PUD->PMD->PTE中間的PUD/PMD被省略的，pmd_off_k的返回值實際就是pgd_offset_k。
arch\arm\mm\mm.h: static inline pmd_t *pmd_off_k(unsigned long virt) { return pmd_offset(pud_offset(pgd_offset_k(virt), virt), virt); } arch\arm\include\asm\pgtable.h: #define pgd_index(addr) ((addr) >> PGDIR_SHIFT) #define pgd_offset(mm, addr) ((mm)->pgd + pgd_index(addr)) /* to find an entry in a kernel page-table-directory */ #define pgd_offset_k(addr) pgd_offset(&init_mm, addr)--------實際就是addr右移PGDIR_SHIFT位，然后相對於init_mm.pgd即swapper_pg_dir的偏移。swapper_pg_dir是存放內核頁表的地方。
prepare_page_table用於清空頁表項，其實清空了三段地址頁表項，0~MODULES_VADDR、MODULES_VADDR~PAGE_OFFSET、0xef800000~VMALLOC_START。
static inline void prepare_page_table(void) { unsigned long addr; phys_addr_t end; /* * Clear out all the mappings below the kernel image. */ for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE)------------------------清除0~MODULES_VADDR地址段一級頁表。 pmd_clear(pmd_off_k(addr)); #ifdef CONFIG_XIP_KERNEL /* The XIP kernel is mapped in the module area -- skip over it */ addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK; #endif for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE)--------------------------------清除MODULES_VADDR~PAGE_OFFSET地址段一級頁表。 pmd_clear(pmd_off_k(addr)); /* * Find the end of the first block of lowmem. */ end = memblock.memory.regions[0].base + memblock.memory.regions[0].size; if (end >= arm_lowmem_limit)-------------------------------------------------end=0x60000000+0x40000000, arm_lowmem_limit=0x8f800000 end = arm_lowmem_limit; /* * Clear out all the kernel space mappings, except for the first * memory bank, up to the vmalloc region. */ for (addr = __phys_to_virt(end); addr < VMALLOC_START; addr += PMD_SIZE)---------------------------------此處end取0x8f800000，轉成虛擬地址0xef800000。清除0xef800000~VMALLOC_START地址段一級頁表。 pmd_clear(pmd_off_k(addr)); }
真正創建頁表是在map_lowmem創建了兩塊區間映射區間一0x60000000~0x60800000(0xc0000000~0xc0800000)和區間二0x60800000~0x8f800000(0xc0800000~0xef800000)。
區間一：具有讀寫執行權限，主要用於存放Kernel代碼數據段，還包括swapper_pg_dir內容。
區間二：具有讀寫，不允許執行，是Normal Memory部分。
可以看出這兩個區間虛擬到物理地址映射是線性映射，但是存在在末尾存在特殊兩頁不是線性映射。
static void __init map_lowmem(void) { struct memblock_region *reg; phys_addr_t kernel_x_start = round_down(__pa(_stext), SECTION_SIZE); phys_addr_t kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE);--------------kernel_x_start=0x60000000, kernel_x_end=60800000 /* Map all the lowmem memory banks. */ for_each_memblock(memory, reg) { phys_addr_t start = reg->base; phys_addr_t end = start + reg->size;----------------------start=0x60000000, end=0x8f800000 struct map_desc map; if (end > arm_lowmem_limit) end = arm_lowmem_limit;-------------------------------因為arm_lowmem_limit=0x8f800000，所以end=0x8f800000 if (start >= end) break; if (end < kernel_x_start) { map.pfn = __phys_to_pfn(start); map.virtual = __phys_to_virt(start); map.length = end - start; map.type = MT_MEMORY_RWX; create_mapping(&map); } else if (start >= kernel_x_end) { map.pfn = __phys_to_pfn(start); map.virtual = __phys_to_virt(start); map.length = end - start; map.type = MT_MEMORY_RW; create_mapping(&map); } else { /* This better cover the entire kernel */ if (start < kernel_x_start) { map.pfn = __phys_to_pfn(start); map.virtual = __phys_to_virt(start); map.length = kernel_x_start - start; map.type = MT_MEMORY_RW; create_mapping(&map); } map.pfn = __phys_to_pfn(kernel_x_start); map.virtual = __phys_to_virt(kernel_x_start); map.length = kernel_x_end - kernel_x_start; map.type = MT_MEMORY_RWX; create_mapping(&map);--------------創建虛擬地址0xc0000000 - 0xc0800000到物理地址0x60000000 - 0x60800000的映射關系，屬性為MT_MEMORY_RWX。 if (kernel_x_end < end) { map.pfn = __phys_to_pfn(kernel_x_end); map.virtual = __phys_to_virt(kernel_x_end); map.length = end - kernel_x_end; map.type = MT_MEMORY_RW; create_mapping(&map);----------創建虛擬地址0xc0800000 - 0xef800000到物理地址0x60800000 - 0x8f800000的映射關系，屬性為MT_MEMORY_RW。 } } } }
還有一部分內存映射在devicemaps_init中進行，對vectors進行映射：
MT_HIGH_VECTORS：虛擬地址-0xffff0000~0xffff1000，對應物理地址是0x8f7fe000~0x8f7ff000。
MT_LOW_VECTORS：虛擬地址-0xffff1000~0xffff2000，對應的物理地址是0x8f7ff000~0x8f800000。
static void __init devicemaps_init(const struct machine_desc *mdesc) { struct map_desc map; unsigned long addr; void *vectors; printk("%s\n", __func__); /* * Allocate the vector page early. */ vectors = early_alloc(PAGE_SIZE * 2); early_trap_init(vectors); for (addr = VMALLOC_START; addr; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr)); /* * Map the kernel if it is XIP. * It is always first in the modulearea. */ #ifdef CONFIG_XIP_KERNEL map.pfn = __phys_to_pfn(CONFIG_XIP_PHYS_ADDR & SECTION_MASK); map.virtual = MODULES_VADDR; map.length = ((unsigned long)_etext - map.virtual + ~SECTION_MASK) & SECTION_MASK; map.type = MT_ROM; create_mapping(&map); #endif /* * Map the cache flushing regions. */ #ifdef FLUSH_BASE map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS); map.virtual = FLUSH_BASE; map.length = SZ_1M; map.type = MT_CACHECLEAN; create_mapping(&map); #endif #ifdef FLUSH_BASE_MINICACHE map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS + SZ_1M); map.virtual = FLUSH_BASE_MINICACHE; map.length = SZ_1M; map.type = MT_MINICLEAN; create_mapping(&map); #endif /* * Create a mapping for the machine vectors at the high-vectors * location (0xffff0000). If we aren't using high-vectors, also * create a mapping at the low-vectors virtual address. */ map.pfn = __phys_to_pfn(virt_to_phys(vectors)); map.virtual = 0xffff0000; map.length = PAGE_SIZE; #ifdef CONFIG_KUSER_HELPERS map.type = MT_HIGH_VECTORS; #else map.type = MT_LOW_VECTORS; #endif create_mapping(&map);----------將虛擬地址0xffff0000 - 0xffff1000映射到0x8f7fe000 - 0x8f7ff000，屬性為MT_HIGH_VECTORS。 if (!vectors_high()) { map.virtual = 0; map.length = PAGE_SIZE * 2; map.type = MT_LOW_VECTORS; create_mapping(&map);------將虛擬地址0xffff1000 - 0xffff2000映射到0x8f7ff000 - 0x8f800000，屬性為MT_LOW_VECTORS。 } /* Now create a kernel read-only mapping */ map.pfn += 1; map.virtual = 0xffff0000 + PAGE_SIZE; map.length = PAGE_SIZE; map.type = MT_LOW_VECTORS; create_mapping(&map); /* * Ask the machine support to map in the statically mapped devices. */ if (mdesc->map_io) mdesc->map_io(); else debug_ll_io_init(); fill_pmd_gaps(); /* Reserve fixed i/o space in VMALLOC region */ pci_reserve_io(); /* * Finally flush the caches and tlb to ensure that we're in a * consistent state wrt the writebuffer. This also ensures that * any write-allocated cache lines in the vector page are written * back. After this point, we can start to touch devices again. */ local_flush_tlb_all(); flush_cache_all(); }
void __init sanity_check_meminfo(void)
？？？？？這些頁如何保證不會別另作他用？？？？？
4. zone初始化
內存管理將一個內存Node分成若干個zone進行管理，定義zone類型在enum zone_type中。
Vexpress之定義了NORMAL和HIGHMEM兩種，zone的初始化在bootmem_init中進行。通過find_limits找出物理內存開始幀號min_low_pfn、結束幀號max_pfn、NORMAL區域的結束幀號max_low_pfn。
void __init bootmem_init(void) { unsigned long min, max_low, max_high; memblock_allow_resize(); max_low = max_high = 0; find_limits(&min, &max_low, &max_high);----------------------min_now_pfn=0x60000 max_low_pfn=0x8f800 max_pfn=0xa0000，通過全局變量memblock獲取信息 ... zone_sizes_init(min, max_low, max_high);---------------------從min_low_pfn到max_low_pfn是ZONE_NORMAL，max_low_pfn到max_pfn是ZONE_HIGHMEM。 /* * This doesn't seem to be used by the Linux memory manager any * more, but is used by ll_rw_block. If we can get rid of it, we * also get rid of some of the stuff above as well. */ min_low_pfn = min; max_low_pfn = max_low; max_pfn = max_high; }
zone_sizes_init中計算出每個zone大小以及zone之間的hole，然后調用free_area_init_node創建內存節點的zone。
void __paginginit free_area_init_node(int nid, unsigned long *zones_size, unsigned long node_start_pfn, unsigned long *zholes_size) { pg_data_t *pgdat = NODE_DATA(nid);--------------------------------------------獲取nid對應的Node數據結構 unsigned long start_pfn = 0; unsigned long end_pfn = 0; /* pg_data_t should be reset to zero when it's allocated */ WARN_ON(pgdat->nr_zones || pgdat->classzone_idx); pgdat->node_id = nid; pgdat->node_start_pfn = node_start_pfn; ... calculate_node_totalpages(pgdat, start_pfn, end_pfn, zones_size, zholes_size);---------------------------------------計算Node的page數目，1GB/4KB=262144 alloc_node_mem_map(pgdat); #ifdef CONFIG_FLAT_NODE_MEM_MAP printk(KERN_DEBUG "free_area_init_node: node %d, pgdat %08lx, node_mem_map %08lx\n", nid, (unsigned long)pgdat, (unsigned long)pgdat->node_mem_map); #endif free_area_init_core(pgdat, start_pfn, end_pfn, zones_size, zholes_size);----------------------------------------逐個初始化Node中的Zone } static void __paginginit free_area_init_core(struct pglist_data *pgdat, unsigned long node_start_pfn, unsigned long node_end_pfn, unsigned long *zones_size, unsigned long *zholes_size) { enum zone_type j; int nid = pgdat->node_id; unsigned long zone_start_pfn = pgdat->node_start_pfn; int ret; pgdat_resize_init(pgdat); #ifdef CONFIG_NUMA_BALANCING spin_lock_init(&pgdat->numabalancing_migrate_lock); pgdat->numabalancing_migrate_nr_pages = 0; pgdat->numabalancing_migrate_next_window = jiffies; #endif init_waitqueue_head(&pgdat->kswapd_wait); init_waitqueue_head(&pgdat->pfmemalloc_wait); pgdat_page_ext_init(pgdat); for (j = 0; j < MAX_NR_ZONES; j++) { struct zone *zone = pgdat->node_zones + j; unsigned long size, realsize, freesize, memmap_pages; size = zone_spanned_pages_in_node(nid, j, node_start_pfn, node_end_pfn, zones_size); realsize = freesize = size - zone_absent_pages_in_node(nid, j, node_start_pfn, node_end_pfn, zholes_size); /* * Adjust freesize so that it accounts for how much memory * is used by this zone for memmap. This affects the watermark * and per-cpu initialisations */ memmap_pages = calc_memmap_size(size, realsize);--------------------------------計算struct page本省需要耗費的空間大小。 if (!is_highmem_idx(j)) {-------------------------------------------------------HIGHMEM不計算映射耗費page數目。 if (freesize >= memmap_pages) { freesize -= memmap_pages; if (memmap_pages) printk(KERN_DEBUG " %s zone: %lu pages used for memmap\n", zone_names[j], memmap_pages); } else printk(KERN_WARNING " %s zone: %lu pages exceeds freesize %lu\n", zone_names[j], memmap_pages, freesize); } /* Account for reserved pages */ if (j == 0 && freesize > dma_reserve) { freesize -= dma_reserve; printk(KERN_DEBUG " %s zone: %lu pages reserved\n", zone_names[0], dma_reserve); } if (!is_highmem_idx(j)) nr_kernel_pages += freesize; /* Charge for highmem memmap if there are enough kernel pages */ else if (nr_kernel_pages > memmap_pages * 2) nr_kernel_pages -= memmap_pages; nr_all_pages += freesize; zone->spanned_pages = size; zone->present_pages = realsize; /* * Set an approximate value for lowmem here, it will be adjusted * when the bootmem allocator frees pages into the buddy system. * And all highmem pages will be managed by the buddy system. */ zone->managed_pages = is_highmem_idx(j) ? realsize : freesize; #ifdef CONFIG_NUMA zone->node = nid; zone->min_unmapped_pages = (freesize*sysctl_min_unmapped_ratio) / 100; zone->min_slab_pages = (freesize * sysctl_min_slab_ratio) / 100; #endif zone->name = zone_names[j]; spin_lock_init(&zone->lock); spin_lock_init(&zone->lru_lock); zone_seqlock_init(zone); zone->zone_pgdat = pgdat; zone_pcp_init(zone); /* For bootup, initialized properly in watermark setup */ mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages); lruvec_init(&zone->lruvec); if (!size) continue; set_pageblock_order(); setup_usemap(pgdat, zone, zone_start_pfn, size); ret = init_currently_empty_zone(zone, zone_start_pfn, size, MEMMAP_EARLY); BUG_ON(ret); memmap_init(size, nid, j, zone_start_pfn);--------------------------------------- zone_start_pfn += size; } }
上面函數運行結果如下：
On node 0 totalpages: 262144------------------------------------------------262144*4KB=1GB free_area_init_node: node 0, pgdat c0782480, node_mem_map eeffa000 Normal zone: 1520 pages used for memmap-----------------------------------struct page大小32Byte，194560*32B/4KB=1520Page Normal zone: 0 pages reserved Normal zone: 194560 pages, LIFO batch:31----------------------------------194560*4KB=760MB HighMem zone: 67584 pages, LIFO batch:15----------------------------------67584*4KB=264MB
所以ZONE_NORMAL對應的物理地址是0x60000000 - 0x8f800000，ZONE_HIGHMEM對應的物理地址是0x8f800000 - 0xa0000000。
build_all_zonelists_init
ZONE_PADDING()
watermark
每個zone在系統初始化的時候會計算水位值：WMARK_MIN、WMARK_LOW、WMARK_HIGH。這些參數在kswapd回收頁面內存的時候會用到。
enum zone_watermarks { WMARK_MIN, WMARK_LOW, WMARK_HIGH, NR_WMARK }; #define min_wmark_pages(z) (z->watermark[WMARK_MIN]) #define low_wmark_pages(z) (z->watermark[WMARK_LOW]) #define high_wmark_pages(z) (z->watermark[WMARK_HIGH]) struct zone { /* Read-mostly fields */ /* zone watermarks, access with *_wmark_pages(zone) macros */ unsigned long watermark[NR_WMARK]; ... }
計算水位的一個重要參數min_free_kbytes是在init_per_zone_wmark_min中進行的：
mm/page_alloc.c: module_init(init_per_zone_wmark_min)------------------------------------------計算min_free_kbytes=3489 setup_per_zone_wmarks--> __setup_per_zone_wmarks-->--------------------------------------------計算WMARK_HIGH/WMARK_LOW /* * Initialise min_free_kbytes. * * For small machines we want it small (128k min). For large machines * we want it large (64MB max). But it is not linear, because network * bandwidth does not increase linearly with machine size. We use * * min_free_kbytes = 4 * sqrt(lowmem_kbytes), for better accuracy: * min_free_kbytes = sqrt(lowmem_kbytes * 16) * * which yields * * 16MB: 512k * 32MB: 724k * 64MB: 1024k * 128MB: 1448k * 256MB: 2048k * 512MB: 2896k * 1024MB: 4096k * 2048MB: 5792k * 4096MB: 8192k * 8192MB: 11584k * 16384MB: 16384k */ int __meminit init_per_zone_wmark_min(void) { unsigned long lowmem_kbytes; int new_min_free_kbytes; lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);--------等於lowmem_kbytes=761100 new_min_free_kbytes = int_sqrt(lowmem_kbytes * 16);----------------761100*16開根號=3489. if (new_min_free_kbytes > user_min_free_kbytes) {------------------user_min_free_kbytes=-1, 所以min_free_kbytes=3489。符合[128B, 64MB] min_free_kbytes = new_min_free_kbytes; if (min_free_kbytes < 128) min_free_kbytes = 128; if (min_free_kbytes > 65536) min_free_kbytes = 65536; } else { pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n", new_min_free_kbytes, user_min_free_kbytes); } setup_per_zone_wmarks(); refresh_zone_stat_thresholds(); setup_per_zone_lowmem_reserve(); setup_per_zone_inactive_ratio(); return 0; }
計算水位值是由__setup_per_zone_wmarks完成的：
static void __setup_per_zone_wmarks(void) { unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);------------min_free_kbytes=3489，所以pages_min=3489/2=872 unsigned long lowmem_pages = 0; struct zone *zone; unsigned long flags; /* Calculate total number of !ZONE_HIGHMEM pages */ for_each_zone(zone) { if (!is_highmem(zone)) lowmem_pages += zone->managed_pages;-----------------------------只計算lowmem，所以lowmem_pages=190273 } for_each_zone(zone) { u64 tmp; spin_lock_irqsave(&zone->lock, flags); tmp = (u64)pages_min * zone->managed_pages; do_div(tmp, lowmem_pages);------------------------------------------Normal：tmp=872*190273/190273=872；Highmem：tmp=872*67584/190273=309 if (is_highmem(zone)) { /* * __GFP_HIGH and PF_MEMALLOC allocations usually don't * need highmem pages, so cap pages_min to a small * value here. * * The WMARK_HIGH-WMARK_LOW and (WMARK_LOW-WMARK_MIN) * deltas controls asynch page reclaim, and so should * not be capped for highmem. */ unsigned long min_pages; min_pages = zone->managed_pages / 1024; min_pages = clamp(min_pages, SWAP_CLUSTER_MAX, 128UL); zone->watermark[WMARK_MIN] = min_pages;-------------------------Highmen：min_pages=67584/1024=66 } else { /* * If it's a lowmem zone, reserve a number of pages * proportionate to the zone's size. */ zone->watermark[WMARK_MIN] = tmp;--------------------------------Normal:872 } zone->watermark[WMARK_LOW] = min_wmark_pages(zone) + (tmp >> 2);----Normal:872+872/4=1090；Highmem：66+309/4=143 zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1);----Normal：872+872/2=1308；Highmem：66+309/2=220 __mod_zone_page_state(zone, NR_ALLOC_BATCH, high_wmark_pages(zone) - low_wmark_pages(zone) - atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH])); setup_zone_migrate_reserve(zone); spin_unlock_irqrestore(&zone->lock, flags); } /* update totalreserve_pages */ calculate_totalreserve_pages(); }
打印每個zone信息如下：
Normal min=872 low=1090 high=1308 zone_start_pfn=393216 managed_pages=190273 spanned_pages=194560 present_pages=194560----大小：0x2f800*4KB=760MB，可用：190273 Page HighMem min=66 low=143 high=220 zone_start_pfn=587776 managed_pages=67584 spanned_pages=67584 present_pages=67584---------大小：0x10800*4KB=264MB，可用：67584 Pagepresent_pages=67584Movable min=32 low=32 high=32 zone_start_pfn=0 managed_pages=0 spanned_pages=0 present_pages=0
5. 物理內存初始化
物理內存頁面需要加入到伙伴系統中，伙伴系統是一種動態存儲管理方法。在用戶提出申請時，分配一塊大小合適的內存塊，反之在釋放時回收內存塊。
伙伴系統分配對空閑頁面的管理是根據兩個屬性：頁的大小，2的order次冪個頁；和頁的遷移類型。
struct zone { ... #ifndef CONFIG_SPARSEMEM /* * Flags for a pageblock_nr_pages block. See pageblock-flags.h. * In SPARSEMEM, this map is stored in struct mem_section */ unsigned long *pageblock_flags;-----------------------------zone中pageblock對應的MIGRATE_TYPE #endif /* CONFIG_SPARSEMEM */... /* free areas of different sizes */ struct free_area free_area[MAX_ORDER];---------------------------按照order區分的空閑頁塊鏈表 ... }
MIGRATE_TYPES
enum { MIGRATE_UNMOVABLE,--------------------頁框內容不可移動，在內存中位置必須固定，無法移動到其它地方，核心內核分配的大部分頁面都屬於這一類。 MIGRATE_RECLAIMABLE,------------------頁框內容可回收，不能直接移動。因為還可以從某些源重建頁面，比如映射文件的數據屬於這種類別，kswapd會按照一定的規則，周期性回收這類頁面。 MIGRATE_MOVABLE,----------------------頁框內容可移動，屬於用戶空間應用程序的頁屬於此類頁面，他們是通過頁表映射的，因此只需要更新頁表項，並把數據復制到新位置就可以了。當然要注意，一個頁面可能被多個進程共享，對應着多個頁表項。 MIGRATE_PCPTYPES, /* the number of types on the pcp lists */-----用來表示每CPU頁框高速緩存的數據結構中的鏈表的遷移類型數目。 MIGRATE_RESERVE = MIGRATE_PCPTYPES, #ifdef CONFIG_CMA /* * MIGRATE_CMA migration type is designed to mimic the way * ZONE_MOVABLE works. Only movable pages can be allocated * from MIGRATE_CMA pageblocks and page allocator never * implicitly change migration type of MIGRATE_CMA pageblock. * * The way to use it is to change migratetype of a range of * pageblocks to MIGRATE_CMA which can be done by * __free_pageblock_cma() function. What is important though * is that a range of pageblocks must be aligned to * MAX_ORDER_NR_PAGES should biggest page be bigger then * a single pageblock. */ MIGRATE_CMA,------------------------預留一段內存給驅動使用，但當驅動不用的時候，伙伴系統可以分配給用戶進程用作匿名內存或者頁緩存。而當驅動需要使用時，就將進程占用的內存通過回收或者遷移的方式將之前占用的預留內存騰出來，供驅動使用。 #endif #ifdef CONFIG_MEMORY_ISOLATION MIGRATE_ISOLATE, /* can't allocate from here */-----------------不能從這個鏈表分配頁框，因為這個鏈表專門用於NUMA節點移動物理內存頁，將物理內存也內容移動到使用這個頁最頻繁的CPU。 #endif MIGRATE_TYPES }
pageblock
#ifdef CONFIG_HUGETLB_PAGE ... #else /* CONFIG_HUGETLB_PAGE */ /* If huge pages are not used, group by MAX_ORDER_NR_PAGES */ #define pageblock_order (MAX_ORDER-1) #endif /* CONFIG_HUGETLB_PAGE */ #define pageblock_nr_pages (1UL << pageblock_order)
CONFIG_NO_BOOTMEM
usemap_size
memmap_init