Thank you Tristan, Mulyadi, > actually given new process address and whole new page tables, but these > page tables is pointing on the COW'ed physical pages of the parents. So in other words, when the child writes onto the physical page COW'ed from the parent, the VM page handler will invalidate that access and copy the parent's physical page frame into another physical page frame and update the child's page table to the NEW PFN. Is this OK? > Are you sure about this Tristan? IMHO every process has a parent, even > it is a thread created on NPTL environment. Perhaps you got this > impression since each thread has same pid? So the task ID of the parent "process" the same as its PID? > Every process/thread has distinct stack area, so there won't be any > overlapping stack area. I am not clear "where" this stack area is being created. Is the stack area of the thread (child thread) created WITHIN the stack area of the parent thread/process with that space allocated just for the childs usage? To put it more clearly, every process has it's own page tables mapping onto physical memory. In its own virtual address space, there is a place for storing its own stack (among other things such as text, code etc). Now, when this process creates a child thread, the thread doesn't have its own address space but it shares all of the address space of the parent. But this address space does not include the stack of the parent since the thread has it;s own stack. So, where does this stack come from? Is it a part of the parent process's own stack that is now being used exclusively by the child thread? > You mean, where it is saved so later it can restored? If this is what > you mean, read about "thread_struct" structure inside the task_struct. > That's where the Stack pointer of current running process is saved > during context switch And the task_struct of each process is stored on the hard disk, is that right? Would I be correct in assuming that the kernel has a pointer to where every process's process descriptor is located/stored on the hard disk? How does the kernel know the PID of a process without first having its PD? > I don't understand about your question "which registers are popped from > stack?" If what you mean, is there something popped from (kernel?) > stack, then the answer no...nothing is popped from kernel stack. So all the kernel variables "Stay" in the kernel stack all the time and so do their mappings into virtual memory? > In short, yes...two or more processes can share same physical pages. The > possibilities are: > 1. Those processes use the same shared libraries > 2. on COW scenario You mean "before" the pages are written onto, right? Thank you again for the tremendous help, Tristan and Mulyadi. - TD -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
