Pintos 2020

Project 1: Threads

• Handle the sleep action by checking all threads when interrupt happened.
• Priority Schedule: Fetch the max priority thread by scanning all threads.
• Execute thread preempt when create thread and priority changed.
• Priority Donate:
  • Holder's priority should bigger than the waiter's priority
  • Save the max priority of all waiters in struct_lock as max_priority
  • Every thread save the max max_priority of all hold lock.
  • Update information at lock changed.
• Follow the tutorial to implement dynamic priority.

Project 2: User Programs

• Get and pass arguments with the stack pointer.
• Check the address carefully, not just the starting address.
• Handle the syscalls with the base filesystem.
• The most tricky part is the process wait and the return status.
• Use semaphores to assure the values pass correctly.

Project 3: Virtual Memory

• Frame Table
  • Maintain a hash table that translates a page to a frame.
  • Allocate frames from the user pool if available.
  • When a frame replacement is necessary, use clock algorithm to evict frames efficiently.
  • Well designed lock mechanism, only lock when necessary.
• Supplemental Page Table
  • Maintains a hash table from virtual address to physical address.
  • Records whether the corresponding address is on the physical memory / swap / file.
  • Perfectly designed lock mechanism, only lock when necessary.
  • Able to handle page fault and grows the stack if deemed necessary.
  • Used for checking if a virtual address resides in the user address space and if it's a valid address.
• Swap Table
  • Uses BLOCK_SWAP block device.
  • Utilizes bitmap for fast lookup of currently available slots.
• Memory Mapped Files
  • Maps files onto memory addresses by maintaining a mmap list in each process.
  • Works together with supplemental page table. Mmap list provides a translation from file to virtual address while supplemental page table translates it to the physical address.

Project 4: File Systems

• Cache : Clock algorithm
• Extensible Files.
  • Use a doubly indirect inode to support a maximum 8MB file.
  • Well designed get_set function to handle byte to sector.
  • Well designed file_extend to support writing extra bytes and file allocation elegantly.
• Subdirectory : Save the parent directory in first file. (unavailable in root '/')