Linux的内存布局

T he 4 GB address space in 32 bit x86 Linux is usually split into different sections for every process on

the system:

0GB-1GB User space - Used for text, code and brk/sbrk allocations. malloc uses brk for small

chunks.

1GB-3GB User space - Used for shared libraries, shared memory, and the stack. Shared memory

and malloc use mmap. malloc uses mmap for large chunks.

3GB-4GB Kernel Space - Used by and for the kernel itself

The split between brk(2) and mmap(2) was changed by setting the kernel parameter TASK_UNMAPPED_BASE

and by recompiling the kernel.

在x86里，

#define TASK_UNMAPPED_BASE      (PAGE_ALIGN(TASK_SIZE / 3))

The mmap allocated memory grow bottom up from 1GB and the stack grows top down from around 3GB.

The split between user space and kernel space is set by the kernel parameter PAGE_OFFSET which is usually

0xc0000000 (3GB).

By default, in Red Hat Enterprise Linux 2.1 the address space between 0x4 0000000 (1 GB) and

0xc0000000 (3 GB) is available for mapping shared libraries and shared memory segments. The

default mapped base for loading shared libraries is 0x4 0000000 (1 GB) .