Linux Virtual Memory Layout
Wtual Memory Spice Purpose
| FFJf8000 .FFFFFFFF | copy_user_page / clear_user_page use |
| FFFFI000 - FFFF7FFF | Reserved. P’atforms must not e this address raige. |
| FFFF0000 - FFFFOFFF | Cpu vector |
| FFC00000 - FFFEFFFF | DMA memory mapping region. |
| FF000000- FFBFFFFF | — Reserved fcw future expansion & DMA mappil reØon |
| VMALLOC_END. FEFFFFFF | Free for platform usee, recommended. |
| VMALLOC_START - YMALLOC_END -1. | vmalloco/ loremap() space |
| PAGE_OFFSET - VMALLOC_START -1 | Kernel direct-mped RAM region |
| TASK_SIZE - FGE_0FFSET .1 | Kernel modie space |
| 0000i000 - TASK_SIZE -i | User space mappings |
| 00000000 - 00000FFF | Cpu vector page / null pointer trAP |
| 66 | 几个重要的 分界线 |
See linuy./incluc/asrn.arm/memo,yh for following definitions
deflne TASK_SIZE (Oxbt000000UL)
#detlne PAGE_OFFSET (Oxc0000000UL)
#define VMAI.LOC_START (((unsigned Iong)hii_memory + VMALLOC_OFFSET) & -(lMALLOC_OFFSET-i))
#define VMAU.OC_END (OxE0000000)
| 66 总结pdf from
读后感 | • The virtual address space of Linux is divided into two parts Ox00000000 to PAGE_OFFSET-i can be for process user space. PAGE_OFFSET to Oxifififif can be addressed only In kernel mode, PAGE_OFFSF1 Is usually Oxc00000000
•ln kernel mode, Linux Physical RAM address have a constant offset to virtual address, the constant is PAGE_OFFSET PHYS_OFFSET.
•Linux Kernel spIel physical memory into page, page size usually 4KB size, Linux physical memory management Is Page-based.
•The boot-time allocator is kernel boot-time page allocator, It allocate physical contiguous page. Boot- time allocator is destroyed when buddy system initialized.
•The buddy system the kernel core page allocator. it allocate physical conteguoLs page
•The slab system Is a cached object pro-allocated system, slab call buddy page allocator to buikng a slab, a slab Is one or more physical contiguous page , contain many pro-allocated objects.
Kmalloc return object in physical contiguous addrres
•vmalloc is usefull when need virtual contiguous page only.
•loremap Is not allocator, It only map specIal physical address to a virtual address, usually for I/O registers. You should access the address wIth wrlteb/readb/wrltew/readw.
| 什么时候需要 连续的内存（物理），in kernel
A:查代码 哪儿用了，呵呵 .
有ioremap 介绍 （浅） |