linux virtual memory layout by moniskiller upload [读书笔记]

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.