+---------------------------+ | CS 140 | | PROJECT 3: VIRTUAL MEMORY | | DESIGN DOCUMENT | +---------------------------+ ---- GROUP ---- >> Fill in the names and email addresses of your group members. FirstName LastName <email@domain.example> FirstName LastName <email@domain.example> FirstName LastName <email@domain.example> ---- PRELIMINARIES ---- >> If you have any preliminary comments on your submission, notes for the >> TAs, or extra credit, please give them here. >> Please cite any offline or online sources you consulted while >> preparing your submission, other than the Pintos documentation, course >> text, lecture notes, and course staff. PAGE TABLE MANAGEMENT ===================== ---- DATA STRUCTURES ---- >> A1: Copy here the declaration of each new or changed `struct' or >> `struct' member, global or static variable, `typedef', or >> enumeration. Identify the purpose of each in 25 words or less. ---- ALGORITHMS ---- >> A2: In a few paragraphs, describe your code for locating the frame, >> if any, that contains the data of a given page. >> A3: How does your code coordinate accessed and dirty bits between >> kernel and user virtual addresses that alias a single frame, or >> alternatively how do you avoid the issue? ---- SYNCHRONIZATION ---- >> A4: When two user processes both need a new frame at the same time, >> how are races avoided? ---- RATIONALE ---- >> A5: Why did you choose the data structure(s) that you did for >> representing virtual-to-physical mappings? PAGING TO AND FROM DISK ======================= ---- DATA STRUCTURES ---- >> B1: Copy here the declaration of each new or changed `struct' or >> `struct' member, global or static variable, `typedef', or >> enumeration. Identify the purpose of each in 25 words or less. ---- ALGORITHMS ---- >> B2: When a frame is required but none is free, some frame must be >> evicted. Describe your code for choosing a frame to evict. >> B3: When a process P obtains a frame that was previously used by a >> process Q, how do you adjust the page table (and any other data >> structures) to reflect the frame Q no longer has? >> B4: Explain your heuristic for deciding whether a page fault for an >> invalid virtual address should cause the stack to be extended into >> the page that faulted. ---- SYNCHRONIZATION ---- >> B5: Explain the basics of your VM synchronization design. In >> particular, explain how it prevents deadlock. (Refer to the >> textbook for an explanation of the necessary conditions for >> deadlock.) >> B6: A page fault in process P can cause another process Q's frame >> to be evicted. How do you ensure that Q cannot access or modify >> the page during the eviction process? How do you avoid a race >> between P evicting Q's frame and Q faulting the page back in? >> B7: Suppose a page fault in process P causes a page to be read from >> the file system or swap. How do you ensure that a second process Q >> cannot interfere by e.g. attempting to evict the frame while it is >> still being read in? >> B8: Explain how you handle access to paged-out pages that occur >> during system calls. Do you use page faults to bring in pages (as >> in user programs), or do you have a mechanism for "locking" frames >> into physical memory, or do you use some other design? How do you >> gracefully handle attempted accesses to invalid virtual addresses? ---- RATIONALE ---- >> B9: A single lock for the whole VM system would make >> synchronization easy, but limit parallelism. On the other hand, >> using many locks complicates synchronization and raises the >> possibility for deadlock but allows for high parallelism. Explain >> where your design falls along this continuum and why you chose to >> design it this way. MEMORY MAPPED FILES =================== ---- DATA STRUCTURES ---- >> C1: Copy here the declaration of each new or changed `struct' or >> `struct' member, global or static variable, `typedef', or >> enumeration. Identify the purpose of each in 25 words or less. ---- ALGORITHMS ---- >> C2: Describe how memory mapped files integrate into your virtual >> memory subsystem. Explain how the page fault and eviction >> processes differ between swap pages and other pages. >> C3: Explain how you determine whether a new file mapping overlaps >> any existing segment. ---- RATIONALE ---- >> C4: Mappings created with "mmap" have similar semantics to those of >> data demand-paged from executables, except that "mmap" mappings are >> written back to their original files, not to swap. This implies >> that much of their implementation can be shared. Explain why your >> implementation either does or does not share much of the code for >> the two situations. SURVEY QUESTIONS ================ Answering these questions is optional, but it will help us improve the course in future quarters. Feel free to tell us anything you want--these questions are just to spur your thoughts. You may also choose to respond anonymously in the course evaluations at the end of the quarter. >> In your opinion, was this assignment, or any one of the three problems >> in it, too easy or too hard? Did it take too long or too little time? >> Did you find that working on a particular part of the assignment gave >> you greater insight into some aspect of OS design? >> Is there some particular fact or hint we should give students in >> future quarters to help them solve the problems? Conversely, did you >> find any of our guidance to be misleading? >> Do you have any suggestions for the TAs to more effectively assist >> students, either for future quarters or the remaining projects? >> Any other comments?