第357页 Memory Regions

vm_area_struct: http://lxr.free-electrons.com/source/include/linux/mm_types.h#L256
Memory regions owned by a process never overlap, and the kernel tries to merge regions when a new one is allocated right next to an existing one. Two adjacent regions can be merged if their access rights match.


The map_count field of the memory descriptor contains the number of regions owned by the process. By default, a process may own up to 65,536 different memory regions; however, the system administrator may change this limit by writing in the /proc/sys/vm/max_map_count file.

在我的ubuntu 14.04 上，这个数值是65530
A frequent operation performed by the kernel is to search the memory region that includes a specific linear address.
具体进行哪些操作的时候需要查找memory region ?

The head of the red-black tree is referenced by the mm_rb field of the memory descriptor. Each memory region object stores the color of the node, as well as the pointers to the parent, the left child, and the right child, in the vm_rb field of type rb_node.

最新的rb_node的定义: http://lxr.free-electrons.com/source/include/linux/rbtree.h#L35
在2.6.11版本，也就是本书所采用的版本的结构是：

struct rb_node
{
  struct rb_node *rb_parent;
  int rb_color;
#define RB_RED    0
#define RB_BLACK  1
  struct rb_node *rb_right;
  struct rb_node *rb_left;
};
rb_color 应该是被encoded到parent指针里了，可以省4个字节