Finish that thought.

[pintos-anon] / doc / vm.texi

diff --git a/doc/vm.texi b/doc/vm.texi
index e4f463f5109df8e42c887f9b9aa6c587f1f61bfa..260f9d99c751fce1a3c211e04cbd9119be7f202a 100644 (file)
--- a/doc/vm.texi
+++ b/doc/vm.texi
@@ -273,15 +273,25 @@ 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
+in @bibref{IA32-v3}, and in practice it is probably easier to add a new
+data structure.
 
 @item
 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
@@ -291,8 +301,9 @@ The page fault handler, @func{page_fault} in
 @item
 Locate the page backing the virtual
 address that faulted.  It might be in the file system, in swap,
-already be in physical memory and just not set up in the page table,
 or it might be an invalid virtual address.
+If you implement sharing, it might even
+already be in physical memory and just not set up in the page table,
 
 If the virtual address is invalid, that is, if there's nothing
 assigned to go there, or if the virtual address is above
@@ -363,6 +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