Linux物理内存管理区初始化
Linux物理内存管理区初始化
Linux物理内存管理区在start_kernel函数中进行初始化,此时启动分配器已经建立,所以可以从bootmem中分配需要的内存。
一、全局变量初始化
max_pfn:最大物理页面帧号
start_kernel()->setup_arch()->e820_end_of_ram_pfn()找出最大可用内存页面帧号。
- void __init setup_arch(char **cmdline_p)
- {
- ……
- /*
- * partially used pages are not usable - thus
- * we are rounding upwards:
- */
- /*遍历e820.map,找到系统中得最大内存数,
- 这个内存数需小于4G*/
- max_pfn = e820_end_of_ram_pfn();
- ……
- }
- unsigned long __init e820_end_of_ram_pfn(void)
- {
- /*MAX_ARCH_PFN为4G空间*/
- return e820_end_pfn(MAX_ARCH_PFN, E820_RAM);
- }
- /*
- * Find the highest page frame number we have available
- */
- static unsigned long __init e820_end_pfn(unsigned long limit_pfn, unsigned type)
- {
- int i;
- unsigned long last_pfn = 0;
- unsigned long max_arch_pfn = MAX_ARCH_PFN;/*4G地址空间对应的页面数*/
- /*对e820中所有的内存块,其中e820为从bios中探测到的页面数存放处*/
- for (i = 0; i < e820.nr_map; i++) {
- struct e820entry *ei = &e820.map[i];/*第i个物理页面块*/
- unsigned long start_pfn;
- unsigned long end_pfn;
- if (ei->type != type)/*与找的类型不匹配*/
- continue;
- /*起始地址对应的页面帧号*/
- start_pfn = ei->addr >> PAGE_SHIFT;
- /*结束物理地址对应的页面帧号*/
- end_pfn = (ei->addr + ei->size) >> PAGE_SHIFT;
- if (start_pfn >= limit_pfn)
- continue;
- if (end_pfn > limit_pfn) {
- last_pfn = limit_pfn;/*找到的结束页面帧号大于限制大小时*/
- break;
- }
- if (end_pfn > last_pfn)
- last_pfn = end_pfn;/*保存更新last_pfn*/
- }
- if (last_pfn > max_arch_pfn)/*大于4G空间时*/
- last_pfn = max_arch_pfn;
- /*打印输出信息*/
- printk(KERN_INFO "last_pfn = %#lx max_arch_pfn = %#lx\n",
- last_pfn, max_arch_pfn);
- /*返回最后一个页面帧号*/
- return last_pfn;
- }
max_low_pfn:低端内存最大页面数
start_kernel()->setup_arch()->find_low_pfn_range()
- /*
- * Determine low and high memory ranges:
- */
- /*找到低端内存的做大内存页面数,初始化两个变量*/
- void __init find_low_pfn_range(void)
- {
- /* it could update max_pfn */
- /*当内存的大小本来就小于低端内存的做大页框数时;
- 直接没有高端地址映射*/
- if (max_pfn <= MAXMEM_PFN)
- lowmem_pfn_init();
- else/*这是一般PC机的运行流程,存在高端映射*/
- highmem_pfn_init();
- }
我们直接看具有高端地址空间的部分。
- /*
- * We have more RAM than fits into lowmem - we try to put it into
- * highmem, also taking the highmem=x boot parameter into account:
- */
- /*高端地址空间的页面数可以在启动中进行配置;
- 如果不配置,在这里进行设置大小*/
- void __init highmem_pfn_init(void)
- {
- /*MAXMEM_PFN为最大物理地址-(4M+4M+8K+128M);
- 所以低端内存的大小其实比我们说的896M低一些*/
- max_low_pfn = MAXMEM_PFN;
- if (highmem_pages == -1)/*高端内存页面数如果在开机没有设置*/
- highmem_pages = max_pfn - MAXMEM_PFN;/*总页面数减去低端页面数*/
- /*如果highmem_pages变量在启动项设置了,那么在这里就要进行这样的判断,因为可能出现不一致的情况*/
- if (highmem_pages + MAXMEM_PFN < max_pfn)
- max_pfn = MAXMEM_PFN + highmem_pages;
- if (highmem_pages + MAXMEM_PFN > max_pfn) {
- printk(KERN_WARNING MSG_HIGHMEM_TOO_SMALL,
- pages_to_mb(max_pfn - MAXMEM_PFN),
- pages_to_mb(highmem_pages));
- highmem_pages = 0;
- }
- #ifndef CONFIG_HIGHMEM
- /* Maximum memory usable is what is directly addressable */
- printk(KERN_WARNING "Warning only %ldMB will be used.\n", MAXMEM>>20);
- if (max_pfn > MAX_NONPAE_PFN)
- printk(KERN_WARNING "Use a HIGHMEM64G enabled kernel.\n");
- else
- printk(KERN_WARNING "Use a HIGHMEM enabled kernel.\n");
- max_pfn = MAXMEM_PFN;
- #else /* !CONFIG_HIGHMEM *//*存在高端地址情况*/
- #ifndef CONFIG_HIGHMEM64G
- /*在没有配置64G的情况下,内存的大小不能超过4G*/
- if (max_pfn > MAX_NONPAE_PFN) {
- max_pfn = MAX_NONPAE_PFN;
- printk(KERN_WARNING MSG_HIGHMEM_TRIMMED);
- }
- #endif /* !CONFIG_HIGHMEM64G */
- #endif /* !CONFIG_HIGHMEM */
- }
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