On 9/1/05, Thayumanavar Sachithanantham <thayumker@xxxxxxxxx> wrote: > When the terms "user space" and "kernel space" are used, do they refer to > the physical memory of the machine (RAM, actually present) or to the virtual > memory (4 GB on 32-bit machines, just virtual) ? > > The term kernel spacerefer to set of addresses that contain's kernel > code+kernel related structures. In most OS such as linux,the kernel space > can't be swapped or paged out. > The user space refers to an area of the memory used by user mode > applications. Depending on > context , this space of addresses could either mean physical or virtual. > AFAIK user space and kernel space always refer to the virtual addresses, and in return these virtual addresses points to the physical addresses through page tables ..... And User Space and Kernel Space Addresses (Virtual) are different b/c they must not be able to interact directly or by mistake and this is due to the proctection level of the processor and system ...... > > I have read somewhere, that kernel threads always have "mm" member of > >their task_struct pointing to "NULL" (task.mm->NULL). Is that correct? > > The task.mm is NULL because a kernel thread never accesses the user space > portion. > And also in kernel the address space is same so no need to make different mm for each thread in kernel (this reduces context switching too (CMIIW) ) ......... -- Fawad Lateef -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
