Clarify.

[pintos-anon] / doc / vm.texi

diff --git a/doc/vm.texi b/doc/vm.texi
index e4f463f5109df8e42c887f9b9aa6c587f1f61bfa..ef2eb80050c77efc5b08cdc5da6f6696e35aed2d 100644 (file)
--- a/doc/vm.texi
+++ b/doc/vm.texi
@@ -278,6 +278,12 @@ 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
@@ -291,8 +297,9 @@ 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