Memory: 1031428K/1048576K available (4787K kernel code, 156K rwdata, 1364K rodata, 1348K init, 166K bss, 17148K reserved, 0K cma-reserved, 270336K highmem)Virtual kernel memory layout:    vector  : 0xffff0000 - 0xffff1000   (   4 kB)    fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)    vmalloc : 0xf0000000 - 0xff000000   ( 240 MB)    lowmem  : 0xc0000000 - 0xef800000   ( 760 MB)    pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB)    modules : 0xbf000000 - 0xbfe00000   (  14 MB)      .text : 0xc0008000 - 0xc060a09c   (6153 kB)      .init : 0xc060b000 - 0xc075c000   (1348 kB)      .data : 0xc075c000 - 0xc07833c0   ( 157 kB)       .bss : 0xc07833c0 - 0xc07acbf0   ( 167 kB)

void __init mem_init(void){#ifdef CONFIG_HAVE_TCM    /* These pointers are filled in on TCM detection */    extern u32 dtcm_end;    extern u32 itcm_end;#endif    set_max_mapnr(pfn_to_page(max_pfn) - mem_map);    /* this will put all unused low memory onto the freelists */    free_unused_memmap();    free_all_bootmem();#ifdef CONFIG_SA1111    /* now that our DMA memory is actually so designated, we can free it */    free_reserved_area(__va(PHYS_OFFSET), swapper_pg_dir, -1, NULL);#endif    free_highpages();    mem_init_print_info(NULL);#define MLK(b, t) b, t, ((t) - (b)) >> 10#define MLM(b, t) b, t, ((t) - (b)) >> 20#define MLK_ROUNDUP(b, t) b, t, DIV_ROUND_UP(((t) - (b)), SZ_1K)    pr_notice("Virtual kernel memory layout:\n"            "    vector  : 0x%08lx - 0x%08lx   (%4ld kB)\n"#ifdef CONFIG_HAVE_TCM            "    DTCM    : 0x%08lx - 0x%08lx   (%4ld kB)\n"            "    ITCM    : 0x%08lx - 0x%08lx   (%4ld kB)\n"#endif            "    fixmap  : 0x%08lx - 0x%08lx   (%4ld kB)\n"            "    vmalloc : 0x%08lx - 0x%08lx   (%4ld MB)\n"            "    lowmem  : 0x%08lx - 0x%08lx   (%4ld MB)\n"#ifdef CONFIG_HIGHMEM            "    pkmap   : 0x%08lx - 0x%08lx   (%4ld MB)\n"#endif#ifdef CONFIG_MODULES            "    modules : 0x%08lx - 0x%08lx   (%4ld MB)\n"#endif            "      .text : 0x%p" " - 0x%p" "   (%4td kB)\n"            "      .init : 0x%p" " - 0x%p" "   (%4td kB)\n"            "      .data : 0x%p" " - 0x%p" "   (%4td kB)\n"            "       .bss : 0x%p" " - 0x%p" "   (%4td kB)\n",            MLK(UL(CONFIG_VECTORS_BASE), UL(CONFIG_VECTORS_BASE) +                (PAGE_SIZE)),#ifdef CONFIG_HAVE_TCM            MLK(DTCM_OFFSET, (unsigned long) dtcm_end),            MLK(ITCM_OFFSET, (unsigned long) itcm_end),#endif            MLK(FIXADDR_START, FIXADDR_END),            MLM(VMALLOC_START, VMALLOC_END),            MLM(PAGE_OFFSET, (unsigned long)high_memory),#ifdef CONFIG_HIGHMEM            MLM(PKMAP_BASE, (PKMAP_BASE) + (LAST_PKMAP) *                (PAGE_SIZE)),#endif#ifdef CONFIG_MODULES            MLM(MODULES_VADDR, MODULES_END),#endif            MLK_ROUNDUP(_text, _etext),            MLK_ROUNDUP(__init_begin, __init_end),            MLK_ROUNDUP(_sdata, _edata),            MLK_ROUNDUP(__bss_start, __bss_stop));#undef MLK#undef MLM#undef MLK_ROUNDUP    /*     * Check boundaries twice: Some fundamental inconsistencies can     * be detected at build time already.     */#ifdef CONFIG_MMU    BUILD_BUG_ON(TASK_SIZE                > MODULES_VADDR);    BUG_ON(TASK_SIZE                 > MODULES_VADDR);#endif#ifdef CONFIG_HIGHMEM    BUILD_BUG_ON(PKMAP_BASE + LAST_PKMAP * PAGE_SIZE > PAGE_OFFSET);    BUG_ON(PKMAP_BASE + LAST_PKMAP * PAGE_SIZE    > PAGE_OFFSET);#endif    if (PAGE_SIZE >= 16384 && get_num_physpages() <= 128) {        extern int sysctl_overcommit_memory;        /*         * On a machine this small we won't get         * anywhere without overcommit, so turn         * it on by default.         */        sysctl_overcommit_memory = OVERCOMMIT_ALWAYS;    }}

/* PAGE_OFFSET - the virtual address of the start of the kernel image */#define PAGE_OFFSET        UL(CONFIG_PAGE_OFFSET)#define CONFIG_PAGE_OFFSET 0xC0000000

OUTPUT_ARCH(arm)ENTRY(stext)jiffies = jiffies_64;SECTIONS{ /*     * XXX: The linker does not define how output sections are     * assigned to input sections when there are multiple statements     * matching the same input section name.  There is no documented     * order of matching.     *     * unwind exit sections must be discarded before the rest of the     * unwind sections get included.     */... . = 0xC0000000 + 0x00008000; .head.text : {  _text = .;  *(.head.text) } .text : { /* Real text segment        */  _stext = .; /* Text and read-only data    */... }

c0008000 T _textc0008000 T stext...c060a09c T _etextc060b000 T __init_begin...c075c000 D __init_endc075c000 D _datac075c000 D _sdatac075c000 D init_thread_unionc075e000 D __nosave_begin...c07833c0 B __bss_startc07833c0 D _edata..c07acbf0 B __bss_stopc07acbf0 B _end

#define VMALLOC_OFFSET        (8*1024*1024)#define VMALLOC_START        (((unsigned long)high_memory + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1))#define VMALLOC_END        0xff000000UL

static void * __initdata vmalloc_min =    (void *)(VMALLOC_END - (240 << 20) - VMALLOC_OFFSET);----------------------------vmalloc_min为VMALLOC_END向下偏移240MB。void __initsanity_check_meminfo(void){    phys_addr_t memblock_limit = 0;    int highmem = 0;    phys_addr_t vmalloc_limit = __pa(vmalloc_min - 1) + 1;    struct memblock_region *reg;    for_each_memblock(memory, reg) {        phys_addr_t block_start = reg->base;        phys_addr_t block_end = reg->base + reg->size;        phys_addr_t size_limit = reg->size;        if (reg->base >= vmalloc_limit)            highmem = 1;        else            size_limit = vmalloc_limit - reg->base;...        if (!highmem) {            if (block_end > arm_lowmem_limit) {                if (reg->size > size_limit)                    arm_lowmem_limit = vmalloc_limit;------------------------------此种情况arm_lowmem_limit等于vmalloc_min                else                    arm_lowmem_limit = block_end;            }...        }    }    high_memory = __va(arm_lowmem_limit - 1) + 1;---------------------------------所以high_memory也即vmalloc_min。...   memblock_set_current_limit(memblock_limit);-----------------------------------根据arm_lowmem_limit来作为ZONE_NORMAL的终点。}

staticvoid __init find_limits(unsignedlong *min, unsignedlong *max_low,                   unsigned long *max_high){    *max_low = PFN_DOWN(memblock_get_current_limit());    *min = PFN_UP(memblock_start_of_DRAM());    *max_high = PFN_DOWN(memblock_end_of_DRAM());}void __init_memblock memblock_set_current_limit(phys_addr_t limit){    memblock.current_limit = limit;}phys_addr_t __init_memblock memblock_get_current_limit(void){    return memblock.current_limit;}

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;}

arch/arm/kernel/head.S：/* * swapper_pg_dir is the virtual address of the initial page table. * We place the page tables 16K below KERNEL_RAM_VADDR.  Therefore, we must * make sure that KERNEL_RAM_VADDR is correctly set.  Currently, we expect * the least significant 16 bits to be 0x8000, but we could probably * relax this restriction to KERNEL_RAM_VADDR >= PAGE_OFFSET + 0x4000. */#define KERNEL_RAM_VADDR    (PAGE_OFFSET + TEXT_OFFSET)#if (KERNEL_RAM_VADDR & 0xffff) != 0x8000--------------------------------------KERNEL_RAM_VADDR也确实是0xc0008000#error KERNEL_RAM_VADDR must start at 0xXXXX8000#endif#ifdef CONFIG_ARM_LPAE    /* LPAE requires an additional page for the PGD */#define PG_DIR_SIZE    0x5000#define PMD_ORDER    3#else#define PG_DIR_SIZE    0x4000#define PMD_ORDER    2#endif    .globl    swapper_pg_dir    .equ    swapper_pg_dir, KERNEL_RAM_VADDR - PG_DIR_SIZE-------------------.equ定义swapper_pg_dir的绝对地址，所以swapper_pg_dir=0xc0008000-0x4000=0xc0004000mm/init-mm.c：struct mm_struct init_mm = {    .mm_rb        = RB_ROOT,    .pgd        = swapper_pg_dir,...    INIT_MM_CONTEXT(init_mm)};

#define FIXADDR_START        0xffc00000UL#define FIXADDR_END        0xfff00000UL#define FIXADDR_TOP        (FIXADDR_END - PAGE_SIZE)-------------保留一页Hole

#define CONFIG_VECTORS_BASE 0xffff0000

    __vectors_start = .;    .vectors 0 : AT(__vectors_start) {        *(.vectors)    }    . = __vectors_start + SIZEOF(.vectors);    __vectors_end = .;    __stubs_start = .;    .stubs 0x1000 : AT(__stubs_start) {        *(.stubs)    }    . = __stubs_start + SIZEOF(.stubs);    __stubs_end = .;

00000000 t __vectors_start00000024 A cpu_v7_suspend_size0000002c A cpu_ca9mp_suspend_size00001000 t __stubs_start00001004 t vector_rst00001020 t vector_irq000010a0 t vector_dabt00001120 t vector_pabt000011a0 t vector_und00001220 t vector_addrexcptn00001240 t vector_fiq00001240 T vector_fiq_offset...

void __init early_trap_init(void *vectors_base){...    memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);    memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);    kuser_init(vectors_base);    flush_icache_range(vectors, vectors + PAGE_SIZE * 2);    modify_domain(DOMAIN_USER, DOMAIN_CLIENT);...}

#define PKMAP_BASE        (PAGE_OFFSET - PMD_SIZE)---------------------0xc0000000-0x200000=0xbfe00000#define LAST_PKMAP        PTRS_PER_PTE#define PTRS_PER_PTE        512#define PMD_SHIFT        21#define PGDIR_SHIFT        21#define PMD_SIZE        (1UL << PMD_SHIFT)Documentation/arm/memory.txt：PKMAP_BASE    PAGE_OFFSET-1    Permanent kernel mappings One way of mapping HIGHMEM pages into kernel                space. 

/* * The module space lives between the addresses given by TASK_SIZE * and PAGE_OFFSET - it must be within 32MB of the kernel text. */#ifndef CONFIG_THUMB2_KERNEL#define MODULES_VADDR        (PAGE_OFFSET - SZ_16M)------------------0xc0000000-0x1000000=0xbf000000#else/* smaller range for Thumb-2 symbols relocation (2^24)*/#define MODULES_VADDR        (PAGE_OFFSET - SZ_8M)#endif#if TASK_SIZE > MODULES_VADDR#error Top of user space clashes with start of module space#endif/* * The highmem pkmap virtual space shares the end of the module area. */#ifdef CONFIG_HIGHMEM#define MODULES_END        (PAGE_OFFSET - PMD_SIZE)----------------0xc0000000-0x200000=0xbfe00000#else#define MODULES_END        (PAGE_OFFSET)#endif