Unix Memory Management question and answer for interview

36. What is page fault? Its types?
Page fault refers to the situation of not having a page in the main memory when any process references it. There are two types of page fault :

  1. Validity fault,
  2. Protection fault.

37. In what way the Fault Handlers and the Interrupt handlers are different?
Fault handlers are also an interrupt handler with an exception that the interrupt handlers cannot sleep. Fault handlers sleep in the context of the process that caused the memory fault. The fault refers to the running process and no arbitrary processes are put to sleep.

38. What is validity fault?
If a process referring a page in the main memory whose valid bit is not set, it results in validity fault. The valid bit is not set for those pages:

  1. that are outside the virtual address space of a process,
  2. that are the part of the virtual address space of the process but no physical address is assigned to it.

39. What does the swapping system do if it identifies the illegal page for swapping?
If the disk block descriptor does not contain any record of the faulted page, then this causes the attempted memory reference is invalid and the kernel sends a "Segmentation violation" signal to the offending process. This happens when the swapping system identifies any invalid memory reference.

40. What are states that the page can be in, after causing a page fault?

  1. On a swap device and not in memory,
  2. On the free page list in the main memory,
  3. In an executable file,
  4. Marked "demand zero",
  5. Marked "demand fill"

41. In what way the validity fault handler concludes?

  1. It sets the valid bit of the page by clearing the modify bit.
  2. It recalculates the process priority.

42. For which kind of fault the page is checked first?
The page is first checked for the validity fault, as soon as it is found that the page is invalid (valid bit is clear), the validity fault handler returns immediately, and the process incur the validity page fault. Kernel handles the validity fault and the process will incur the protection fault if any one is present.

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Unix Memory Management question and answer for interview