Grammar.

[pintos-anon] / doc / vm.texi

diff --git a/doc/vm.texi b/doc/vm.texi
index 6b07490b56fa8412e0113deac5a47226f7b7c331..544701a5b90844f24588e3d5d7dadc81d0244ec9 100644 (file)
--- a/doc/vm.texi
+++ b/doc/vm.texi
@@ -213,6 +213,9 @@ could check and update the accessed and dirty bits for both addresses.
 Alternatively, the kernel could avoid the problem by only accessing user
 data through the user virtual address.
 
+Other aliases should only arise if you implement sharing, as extra
+credit (@pxref{VM Extra Credit}), or as bugs elsewhere in your code.
+
 @deftypefun bool pagedir_is_dirty (uint32_t *@var{pd}, const void *@var{vpage})
 @deftypefunx bool pagedir_is_accessed (uint32_t *@var{pd}, const void *@var{vpage})
 Returns true if page directory @var{pd} contains a page table entry for
@@ -476,7 +479,7 @@ script, so the code you turn in must properly handle all cases.
 Implement stack growth.  In project 2, the stack was a single page at
 the top of the user virtual address space, and programs were limited to
 that much stack.  Now, if the stack grows past its current size,
-allocate additional page as necessary.
+allocate additional pages as necessary.
 
 Allocate additional pages only if they ``appear'' to be stack accesses.
 Devise a heuristic that attempts to distinguish stack accesses from
@@ -607,6 +610,7 @@ summary of project 2.
 Yes.
 
 @item What extra credit is available?
+@anchor{VM Extra Credit}
 
 You may implement sharing: when multiple processes are created that use
 the same executable file, share read-only pages among those processes
@@ -648,6 +652,12 @@ you like, but it should be the underlying mechanism.
 Also, you can use the @option{-u} option to @command{pintos} to limit
 the size of the user pool, which makes it easy to test your VM
 implementation with various user memory sizes.
+
+@item Data pages might need swap space.  Can I swap them out at process load?
+
+No.  Reading data pages from the executable and writing them to swap
+immediately at program startup is not demand paging.  You need to demand
+page everything (except partial pages).
 @end table
 
 @node Memory Mapped File FAQ