Finish that thought.

[pintos-anon] / doc / vm.texi

diff --git a/doc/vm.texi b/doc/vm.texi
index ef2eb80050c77efc5b08cdc5da6f6696e35aed2d..260f9d99c751fce1a3c211e04cbd9119be7f202a 100644 (file)
--- a/doc/vm.texi
+++ b/doc/vm.texi
@@ -273,11 +273,6 @@ Some way of translating in software from virtual page frames to
 physical page frames.  Consider using a hash table (@pxref{Hash
 Table}).
 
-@item
-Some way of translating from physical page frames back to virtual page
-frames, so that when you evict a physical page from its frame, you can
-invalidate its translation(s).
-
 It is possible to do this translation without adding a new data
 structure, by modifying the code in @file{userprog/pagedir.c}.  However,
 if you do that you'll need to carefully study and understand section 3.7
@@ -288,6 +283,15 @@ data structure.
 Some way of finding a page on disk if it is not in memory.  You won't
 need this data structure until problem 3-2, but planning ahead is a
 good idea.
+
+You can generalize the virtual-to-physical page table, so that it allows
+you to locate a page wherever it is in physical memory or on disk, or
+you can make this a separate table.
+
+@item
+Some way of translating from physical page frames back to virtual page
+frames, so that when you evict a physical page from its frame, you can
+invalidate its translation(s).
 @end itemize
 
 The page fault handler, @func{page_fault} in
@@ -370,6 +374,12 @@ pages less frequently using your algorithm than using some inferior
 page replacement policy.  The canonical example of a poor page
 replacement policy is random replacement.
 
+You must write your code so that we can choose a page replacement policy
+at compile time.  By default, the LRU-like algorithm must be in effect,
+but we must be able to choose random replacement by inserting the line
+@code{#define RANDOM_REPLACEMENT 1} in @file{constants.h}.
+@xref{Conditional Compilation}, for details.
+
 Since you will already be paging from disk, you should implement a
 ``lazy'' loading scheme for new processes.  When a process is created,
 it will not run immediately.  Therefore, it doesn't make sense to load