Operating Systems - Memory Management and File System

Review and Learning Outcomes

• The lecture focuses on completing the topic of Memory Management and beginning the discussion on File Systems.
• Key Topics:
  • Memory Management:
  • Address Translation
  • Flexible Address Translation
  • Efficient Address Translation
  • File System:
  • Disk Scheduling
  • Disk Performance
• Homework 6 key is available on Blackboard.
• Quiz 6 will cover lectures 16-19.
• Exam 2 is scheduled for Tuesday, April 8, covering lectures 11-19. A sample exam is posted on Blackboard.

TLB and Page Table Translation

• The translation process combines the Translation Lookaside Buffer (TLB) with hardware page tables.
• Concepts:
  • Virtual Address → Physical Address conversion using TLB and Page Table.
  • Components:
  • TLB - stores recently used mappings of virtual to physical addresses.
  • Page Table - maps virtual pages to frame numbers in physical memory.
• If the TLB hit occurs, the physical address is obtained quickly; otherwise a page table lookup occurs.

TLB Lookup and Operation

• TLB operates by checking each virtual page number against all TLB entries simultaneously.
• Outcomes:
  • If a match occurs, corresponding physical page frame and permissions are retrieved.
  • In case of a TLB miss, the system performs a hardware multi-level page table lookup to find the physical address.

Addressing Mechanisms in Caches

Virtually Addressed vs. Physically Addressed Caches

• Virtual Addressing:
  • First level cache is accessed using virtual addresses to enhance speed.
  • TLB is queried in parallel to get the physical address in the event of a cache miss.
• Physically Addressed Caches:
  • Use physical addresses exclusively for accessing the cache.
  • Similar processes occur for hits and misses as in virtually addressed caches.

Cache Access Operations

• Virtually Addressed Cache:
  • Access patterns in memory and exception handling for valid/invalid addresses.
• Physically Addressed Cache:
  • Similar access, but the focus is on physical addresses and consistency with physical memory.

Superpages

• Superpages are defined as sets of contiguous pages in physical memory that correspond to a contiguous region of virtual memory.
• The operation of TLB is optimized when virtual pages fall within the superpage, allowing for more efficient address translation.

Summary

• The lecture has concluded the coverage of Memory Management and will transition to the discussion of File Systems.