关于mm_struct结构体

Question

字段atomic_t mm_count;在LKD3有下面的一句话：

When the kernel operates on an address space and needs to
bump its associated reference count, the kernel increments mm_count. Having two counters
enables the kernel to differentiate between the main usage counter (mm_count) and
the number of processes using the address space (mm_users).

究竟什么时候增长mm_count?

Answer 1

We'll try to explain the difference between the use of mm_users and mm_count with an example. Consider a memory descriptor shared by two lightweight processes. Normally, its mm_users field stores the value 2, while its mm_count field stores the value 1 (both owner processes count as one).

If the memory descriptor is temporarily lent to a kernel thread (see the next section), the kernel increases the mm_count field. In this way, even if both lightweight processes die and the mm_users field becomes zero, the memory descriptor is not released until the kernel thread finishes using it because the mm_count field remains greater than zero.

Answer 2

http://bbs.chinaunix.net/thread-1991118-1-1.html

Answer 3

tks，内核线程用的是前一个进程的地址空间

Answer 4

准确的说，所有的内核例程都在一个空间里面。