Process Virtual Memory

Process Virtual Memory

1 Process address space

The process virtual memory address space starts at 0, terminates at Task_size-1, which is the kernel space, the total address space is divided by 3:1, the user process cannot access the kernel space, and if there is no protocol, a user process cannot access the space of other processes.

1.1 Layout of the process address space

A text segment of the current run code

Code of the dynamic library used by the B program

c Storage of global variables and dynamically generated data heap

D Save the stack of local variables and function/procedure calls

e environment variables and command line arguments

F file content mapped to memory mappings in virtual memory space

Each process has a mm_struct that holds the memory management information for the process.

Classic Layouts

Mmap addresses are typically 1/3 of virtual space

New layout

If the stack size is set to Unrestricted, select Use classic layout, otherwise use the new layout

1.2 Memory Map

In Mm_struct, the process virtual space information is represented by multiple regions, each region is described by Vm_area_struct, and a red-black tree is used to quickly find the area before the area when adding an area without having to scan the entire list

void* mmap (void* start,size_t length,int prot,int flags,int fd,off_t offset); int Munmap (void* start,size_t length);

The Mmap function creates a length at the beginning of the virtual address space, and the access rights are defined as prot

Process Virtual Memory