linux2.4.18----18.highmem高端内存

一.总体说明


二.代码分析
2.1 在arch/i386/mm/init.c-->paging_init-->pagetable_init

static void __init pagetable_init (void)
{
    //将ZONE_HIGHMEM部分的页目录表修改一下
    //执行后vaddr=0xffc00000(物理地址1020M)(虚拟地址4092M)
    //0xc0101ff0 :	0x00000000	0x00000000	0x00000000	0x00003063
    vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;        //执行后vaddr=0xffc00000
    fixrange_init(vaddr, 0, pgd_base);                                     -->0xc0101ffc处写入0x00003063

#if CONFIG_HIGHMEM
    //执行后vaddr=0xfe000000(物理地址992M)(虚地址4064M离4G还有32M),end=996M  虚地址(4064M-4068M之间)
    //执行后0xc0101fe0 :	0x00004063	0x00000000	0x00000000	0x00000000
    vaddr = PKMAP_BASE;                                                    -->执行后vaddr=0xfe000000
    fixrange_init(vaddr, vaddr + PAGE_SIZE*LAST_PKMAP, pgd_base);          -->0xc0101fe0处写入0x00004063

    pgd = swapper_pg_dir + __pgd_offset(vaddr);   //vaddr=0xfe000000,其pgd_offset=0x3F8,加法运算时0x3F8*4执行后pgd=0xc0101fe0
    pmd = pmd_offset(pgd, vaddr);                 //在pgtable-2level.h中pmd=pgd,所以执行后pmd=0xc0101fe0
    pte = pte_offset(pmd, vaddr);                 //pte=0xc0004000
    pkmap_page_table = pte;                       //pkmap_pate_talbe=0xc0004000
#endif
}

完成之后页目录表的内容如下:

(gdb) x /1024wx 0xc0101000
...
0xc0101f50 <swapper_pg_dir+3920>:    0x350001e3    0x354001e3    0x358001e3    0x35c001e3
0xc0101f60 <swapper_pg_dir+3936>:    0x360001e3    0x364001e3    0x368001e3    0x36c001e3
0xc0101f70 <swapper_pg_dir+3952>:    0x370001e3    0x374001e3    0x378001e3    0x37c001e3
0xc0101f80 <swapper_pg_dir+3968>:    0x00000000    0x00000000    0x00000000    0x00000000   -->这部分是用作vmalloc的
0xc0101f90 <swapper_pg_dir+3984>:    0x00000000    0x00000000    0x00000000    0x00000000
0xc0101fa0 <swapper_pg_dir+4000>:    0x00000000    0x00000000    0x00000000    0x00000000
0xc0101fb0 <swapper_pg_dir+4016>:    0x00000000    0x00000000    0x00000000    0x00000000
0xc0101fc0 <swapper_pg_dir+4032>:    0x00000000    0x00000000    0x00000000    0x00000000
0xc0101fd0 <swapper_pg_dir+4048>:    0x00000000    0x00000000    0x00000000    0x00000000
0xc0101fe0 <swapper_pg_dir+4064>:    0x00004063    0x00000000    0x00000000    0x00000000    -->这部分是用作highmem的
0xc0101ff0 <swapper_pg_dir+4080>:    0x00000000    0x00000000    0x00000000    0x00003063

2.1 在arch/i386/mm/init.c中L81 paging_init-->kmap_init()

//初始化几个变量kmap_vstart=0xffff5000,kmap_pte=0xc0003fd4,kmap_prot=0x163
void __init kmap_init(void)
{
    unsigned long kmap_vstart;

//FIX_KMAP_BEGIN=9, FIXADDR_TOP=0xffffe000(差2个page到4G),kmap_vstart=(FIXADDR_TOP - ((x) << PAGE_SHIFT))
    kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);       //执行后kmap_vstart=0xffff5000
    kmap_pte = kmap_get_fixmap_pte(kmap_vstart);       //执行后kmap_pte=0xc0003fd4

    kmap_prot = PAGE_KERNEL;
}

2.1 在include/asm/highmem.h中L62

static inline void *kmap(struct page *page)
{
    if (in_interrupt())
        BUG();
//这儿传入参数page=0xc1f56f44,highmem_start_page=0xc1ee0010,所以不能返回直接映射
    if (page < highmem_start_page)    //高端内存在page管理区的地址=0xc1000010+0x38000*68=0xc1ee0010
        return page_address(page);    //如果是直接映射的话,返回page->virtual
    return kmap_high(page);
}

如果是直接映射的话，可直接返回page->virtual

(gdb) p *(struct page*)0xc1000010
$5 = {list = {next = 0xc1000010, prev = 0xc1000010}, mapping = 0x0, index = 0, next_hash = 0x0, count = {counter = 0}, flags = 16384, lru = {next = 0x0, prev = 0x0},
    wait = {lock = {lock = 1, magic = 3735899821}, task_list = {next = 0xc100003c, prev = 0xc100003c}}, pprev_hash = 0x0, buffers = 0x0, virtual = 0xc0000000,  //物理地址0x0
  zone = 0xc02cf9c0 <contig_page_data>}

(gdb) p *(struct page*)0xc1000054
$8 = {list = {next = 0xc1000054, prev = 0xc1000054}, mapping = 0x0, index = 0, next_hash = 0x0, count = {counter = 0}, flags = 16384, lru = {next = 0x0, prev = 0x0},
    wait = {lock = {lock = 1, magic = 3735899821}, task_list = {next = 0xc1000080, prev = 0xc1000080}}, pprev_hash = 0x0, buffers = 0x0, virtual = 0xc0001000,  //物理地址4096
  zone = 0xc02cf9c0 <contig_page_data>}

2.1 在mm/highmem.c中L128

void *kmap_high(struct page *page)
{
    unsigned long vaddr;
    spin_lock(&kmap_lock);
    vaddr = (unsigned long) page->virtual;
    if (!vaddr)
        vaddr = map_new_virtual(page);
    pkmap_count[PKMAP_NR(vaddr)]++;             //pkmap_count[1]由1-->2
    if (pkmap_count[PKMAP_NR(vaddr)] < 2)
        BUG();
    spin_unlock(&kmap_lock);
    return (void*) vaddr;                      //vaddr=0xfe001000
}

下面是参数page的打印

(gdb) p *page 的地址=0xc1f56f44
$11 = {list = {next = 0xf7daf3bc, prev = 0xf7daf3bc}, mapping = 0xf7daf3bc, index = 0, next_hash = 0x0, count = {counter = 3}, flags = 2113,
     lru = {next = 0xc1ed562c, prev = 0xc035b42c <inactive_list>}, wait = {lock = {lock = 1, magic = 3735899821}, task_list = {next = 0xc1f56f70, prev = 0xc1f56f70}},
     pprev_hash = 0xf7e6cc68,  buffers = 0xf7db6700, virtual = 0x0, zone = 0xc02cfb18 <contig_page_data+344>}

*(struct zone_struct*)0xc02cf9c0 -->zone_DMA
*(struct zone_struct*)0xC02CFA6C -->zone_Normal
*(struct zone_struct*)0xc02cfb18  --> zone_HighMem



在mm/highmem.c中

static inline unsigned long map_new_virtual(struct page *page)
{
    unsigned long vaddr;
    int count;

start:
    count = LAST_PKMAP;                                           //count=1024=0x400
    /* Find an empty entry */
    for (;;) {
        last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;   //执行后last_pkmap_nr=1
        if (!last_pkmap_nr) {
            flush_all_zero_pkmaps();
            count = LAST_PKMAP;
        }
        if (!pkmap_count[last_pkmap_nr])                         //现在数组pkmap_count中都是0
            break;    /* Found a usable entry */
        if (--count)
            continue;

        /*
         * Sleep for somebody else to unmap their entries
         */
        {
            DECLARE_WAITQUEUE(wait, current);

            current->state = TASK_UNINTERRUPTIBLE;
            add_wait_queue(&pkmap_map_wait, &wait);
            spin_unlock(&kmap_lock);
            schedule();
            remove_wait_queue(&pkmap_map_wait, &wait);
            spin_lock(&kmap_lock);

            /* Somebody else might have mapped it while we slept */
            if (page->virtual)
                return (unsigned long) page->virtual;

            /* Re-start */
            goto start;
        }
    }
//PKMAP_BASE=0xfe000000UL=4064M(离4G有32M)
//#define PKMAP_ADDR(nr)  (PKMAP_BASE + ((nr) << PAGE_SHIFT))是从4064M开始依次加1个page
    vaddr = PKMAP_ADDR(last_pkmap_nr);            //执行后vaddr=0xfe001000
    set_pte(&(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

    pkmap_count[last_pkmap_nr] = 1;              //last_pkmap_nr=1,pkmap_count[last_pkmap_nr]=1
    page->virtual = (void *) vaddr;              //vaddr0xfe001000

    return vaddr;
}

set_pte前后页表项的数据改变：

(gdb) x /4wx 0xc0004004= &(pkmap_page_table[last_pkmap_nr])
0xc0004004:    0x00000000    0x00000000    0x00000000    0x00000000
(gdb) x /4wx 0xc0004004
0xc0004004:    0x3fffd163    0x00000000    0x00000000    0x00000000