61. What are the phases of swapping
a page from the memory?
Ans: Page stealer finds the page eligible for swapping and places the page number in the list of pages to be swapped. Kernel copies the page to a swap device when necessary and clears the valid bit in the page table entry, decrements the pfdata reference count, and places the pfdata table entry at the end of the free list if its reference count is 0.
Ans: Page stealer finds the page eligible for swapping and places the page number in the list of pages to be swapped. Kernel copies the page to a swap device when necessary and clears the valid bit in the page table entry, decrements the pfdata reference count, and places the pfdata table entry at the end of the free list if its reference count is 0.
62. What is page fault? Its types?
Ans: 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 :
- Validity fault,
- Protection fault.
Ans: 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 :
- Validity fault,
- Protection fault.
63. In what way the Fault Handlers
and the Interrupt handlers are different?
Ans: 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.
Ans: 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.
64. What is validity fault?
Ans: 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:
- that are outside the virtual address space of a process,
- that are the part of the virtual address space of the process but no physical address is assigned to it.
Ans: 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:
- that are outside the virtual address space of a process,
- that are the part of the virtual address space of the process but no physical address is assigned to it.
65. What does the swapping system do if it identifies the illegal page for swapping?
Ans: 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.
66. What are states that the page
can be in, after causing a page fault?
Ans: On a swap device and not in memory, On the free page list in the main memory, In an executable file, Marked “demand zero”, Marked “demand fill”.
Ans: On a swap device and not in memory, On the free page list in the main memory, In an executable file, Marked “demand zero”, Marked “demand fill”.
67. In what way the validity fault
handler concludes?
Ans: It sets the valid bit of the page by clearing the modify bit. It recalculates the process priority.
Ans: It sets the valid bit of the page by clearing the modify bit. It recalculates the process priority.
68. At what mode the fault handler
executes?
Ans: At the Kernel Mode.
Ans: At the Kernel Mode.
69. What do you mean by the
protection fault?
Ans: Protection fault refers to the process accessing the pages, which do not have the access permission. A process also incur the protection fault when it attempts to write a page whose copy on write bit was set during the fork( ) system call.
Ans: Protection fault refers to the process accessing the pages, which do not have the access permission. A process also incur the protection fault when it attempts to write a page whose copy on write bit was set during the fork( ) system call.
70. How the Kernel handles the copy
on write bit of a page, when the bit is set?
Ans: In situations like, where the copy on write bit of a page is set and that page is shared by more than one process, the Kernel allocates new page and copies the content to the new page and the other processes retain their references to the old page. After copying the Kernel updates the page table entry with the new page number. Then Kernel decrements the reference count of the old pfdata table entry. In cases like, where the copy on write bit is set and no processes are sharing the page, the Kernel allows the physical page to be reused by the processes. By doing so, it clears the copy on write bit and disassociates the page from its disk copy (if one exists), because other process may share the disk copy. Then it removes the pfdata table entry from the page-queue as the new copy of the virtual page is not on the swap device. It decrements the swap-use count for the page and if count drops to 0, frees the swap space.
Ans: In situations like, where the copy on write bit of a page is set and that page is shared by more than one process, the Kernel allocates new page and copies the content to the new page and the other processes retain their references to the old page. After copying the Kernel updates the page table entry with the new page number. Then Kernel decrements the reference count of the old pfdata table entry. In cases like, where the copy on write bit is set and no processes are sharing the page, the Kernel allows the physical page to be reused by the processes. By doing so, it clears the copy on write bit and disassociates the page from its disk copy (if one exists), because other process may share the disk copy. Then it removes the pfdata table entry from the page-queue as the new copy of the virtual page is not on the swap device. It decrements the swap-use count for the page and if count drops to 0, frees the swap space.
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