Linux内存初始化（下）

void __init paging_init(void)
{
 phys_addr_t pgd_phys = early_pgtable_alloc();//分配一页大小的物理内存放进pgd
 pgd_t *pgd = pgd_set_fixmap(pgd_phys);

 map_kernel(pgd);//将内核的各个段进行映射 .text .init .data .bss
 map_mem(pgd);//将memblock子系统添加的物理内存进行映射(将物理地址映射到线性区域)

 /*
  * We want to reuse the original swapper_pg_dir so we don't have to
  * communicate the new address to non-coherent secondaries in
  * secondary_entry, and so cpu_switch_mm can generate the address with
  * adrp+add rather than a load from some global variable.
  *
  * To do this we need to go via a temporary pgd.
  */
 cpu_replace_ttbr1(__va(pgd_phys));//切换页表
 memcpy(swapper_pg_dir, pgd, PGD_SIZE);//将新建立的页表内容替换swapper_pg_dir页表内容
 cpu_replace_ttbr1(lm_alias(swapper_pg_dir));

 pgd_clear_fixmap();
 memblock_free(pgd_phys, PAGE_SIZE);

 /*
  * We only reuse the PGD from the swapper_pg_dir, not the pud + pmd
  * allocated with it.
  */
 memblock_free(__pa_symbol(swapper_pg_dir) + PAGE_SIZE,
        SWAPPER_DIR_SIZE - PAGE_SIZE);
}

void __init bootmem_init(void)
{
 unsigned long min, max;

 min = PFN_UP(memblock_start_of_DRAM());
 max = PFN_DOWN(memblock_end_of_DRAM());

 early_memtest(min << PAGE_SHIFT, max << PAGE_SHIFT);

 max_pfn = max_low_pfn = max;

 arm64_numa_init();
 /*
  * Sparsemem tries to allocate bootmem in memory_present(), so must be
  * done after the fixed reservations.
  */
 arm64_memory_present();

 sparse_init();
 zone_sizes_init(min, max);

 memblock_dump_all();
}

enum zone_type {
#ifdef CONFIG_ZONE_DMA
 /*
  * ZONE_DMA is used when there are devices that are not able
  * to do DMA to all of addressable memory (ZONE_NORMAL). Then we
  * carve out the portion of memory that is needed for these devices.
  * The range is arch specific.
  *
  * Some examples
  *
  * Architecture  Limit
  * ---------------------------
  * parisc, ia64, sparc <4G
  * s390   <2G
  * arm   Various
  * alpha  Unlimited or 0-16MB.
  *
  * i386, x86_64 and multiple other arches
  *    <16M.
  */
 ZONE_DMA,
#endif
#ifdef CONFIG_ZONE_DMA32
 /*
  * x86_64 needs two ZONE_DMAs because it supports devices that are
  * only able to do DMA to the lower 16M but also 32 bit devices that
  * can only do DMA areas below 4G.
  */
 ZONE_DMA32,
#endif
 /*
  * Normal addressable memory is in ZONE_NORMAL. DMA operations can be
  * performed on pages in ZONE_NORMAL if the DMA devices support
  * transfers to all addressable memory.
  */
 ZONE_NORMAL,
#ifdef CONFIG_HIGHMEM
 /*
  * A memory area that is only addressable by the kernel through
  * mapping portions into its own address space. This is for example
  * used by i386 to allow the kernel to address the memory beyond
  * 900MB. The kernel will set up special mappings (page
  * table entries on i386) for each page that the kernel needs to
  * access.
  */
 ZONE_HIGHMEM,
#endif
 ZONE_MOVABLE,
#ifdef CONFIG_ZONE_DEVICE
 ZONE_DEVICE,
#endif
 __MAX_NR_ZONES

};

/* memmap is virtually contiguous.  */
#define __pfn_to_page(pfn) (vmemmap + (pfn))
#define __page_to_pfn(page) (unsigned long)((page) - vmemmap)