Process -- user address space and kernel address space

User mode address space

• text： Code segment executable code 、 string literal 、 A read-only variable

• data： Data segment , Global variables already initialized in the mapper

• bss： Store uninitialized global variables in the program

• heap： Heap at runtime , Use in program running malloc Requested memory area

• mmap： Mapping areas for shared libraries and anonymous files

• stack： User process stack

Kernel state address space

• Direct mapping area ： From... In linear space 3G Start with the biggest 896M The range of , Is a direct memory mapped area

• Dynamic memory mapping area ： This area is defined by the kernel function vmalloc To allocate

• Permanent memory mapped area ： This area has access to high-end memory

• Fixed mapping area ： The area and 4G At the top of it is only 4k The isolation belt of , Each address entry serves a specific purpose , Such as ：ACPI_BASE etc.

Process memory space

The user process can only access the virtual address of user space , Cannot access kernel space virtual address
Kernel space is mapped by the kernel , It doesn't change with the process ; Kernel space address has its own page table , User processes have different amount page tables