-From: "Godmar Back" <godmar@gmail.com>
-Subject: thread_yield in irq handler
-To: "Ben Pfaff" <blp@cs.stanford.edu>
-Date: Wed, 22 Feb 2006 22:18:50 -0500
-
-Ben,
-
-you write in your Tour of Pintos:
-
-"Second, an interrupt handler must not call any function that can
-sleep, which rules out thread_yield(), lock_acquire(), and many
-others. This is because external interrupts use space on the stack of
-the kernel thread that was running at the time the interrupt occurred.
-If the interrupt handler tried to sleep and that thread resumed, then
-the two uses of the single stack would interfere, which cannot be
-allowed."
-
-Is the last sentence really true?
-
-I thought the reason that you couldn't sleep is that you would put
-effectively a random thread/process to sleep, but I don't think it
-would cause problems with the kernel stack. After all, it doesn't
-cause this problem if you call thread_yield at the end of
-intr_handler(), so why would it cause this problem earlier.
-
-As for thread_yield(), my understanding is that the reason it's called
-at the end is to ensure it's done after the interrupt is acknowledged,
-which you can't do until the end because Pintos doesn't handle nested
-interrupts.
-
- - Godmar
-
-From: "Godmar Back" <godmar@gmail.com>
-
-For reasons I don't currently understand, some of our students seem
-hesitant to include each thread in a second "all-threads" list and are
-looking for ways to implement the advanced scheduler without one.
-
-Currently, I believe, all tests for the mlfqs are such that all
-threads are either ready or sleeping in timer_sleep(). This allows for
-an incorrect implementation in which recent-cpu and priorities are
-updated only for those threads that are on the alarm list or the ready
-list.
-
-The todo item would be a test where a thread is blocked on a
-semaphore, lock or condition variable and have its recent_cpu decay to
-zero, and check that it's scheduled right after the unlock/up/signal.
-
-From: "Godmar Back" <godmar@gmail.com>
-Subject: set_priority & donation - a TODO item
-To: "Ben Pfaff" <blp@cs.stanford.edu>
-Date: Mon, 20 Feb 2006 22:20:26 -0500
-
-Ben,
-
-it seems that there are currently no tests that check the proper
-behavior of thread_set_priority() when called by a thread that is
-running under priority donation. The proper behavior, I assume, is to
-temporarily drop the donation if the set priority is higher, and to
-reassume the donation should the thread subsequently set its own
-priority again to a level that's lower than a still active donation.
-
- - Godmar
-
-From: Godmar Back <godmar@gmail.com>
-Subject: project 4 question/comment regarding caching inode data
-To: Ben Pfaff <blp@cs.stanford.edu>
-Date: Sat, 14 Jan 2006 15:59:33 -0500
-
-Ben,
-
-in section 6.3.3 in the P4 FAQ, you write:
-
-"You can store a pointer to inode data in struct inode, if you want,"
-
-Should you point out that if they indeed do that, they likely wouldn't
-be able to support more than 64 open inodes systemwide at any given
-point in time.
-
-(This seems like a rather strong limitation; do your current tests
-open more than 64 files?
-It would also point to an obvious way to make the projects harder by
-specifically disallowing that inode data be locked in memory during
-the entire time an inode is kept open.)
-
- - Godmar
+Godmar says:
+
+- In Project 2, we're missing tests that pass arguments to system calls
+that span multiple pages, where some are mapped and some are not.
+An implementation that only checks the first page, rather than all pages
+that can be touched during a call to read()/write() passes all tests.
+
+- Need some tests that test that illegal accesses lead to process
+termination. I have written some, will add them. In P2, obviously,
+this would require that the students break this functionality since
+the page directory is initialized for them, still it would be good
+to have.
+
+- There does not appear to be a test that checks that they close all
+fd's on exit. Idea: add statistics & self-diagnostics code to palloc.c
+and malloc.c. Self-diagnostics code could be used for debugging.
+The statistics code would report how much kernel memory is free.
+Add a system call "get_kernel_memory_information". User programs
+could engage in a variety of activities and notice leaks by checking
+the kernel memory statistics.