physical page frames. Pintos provides a hash table that you may find
useful for this purpose (@pxref{Hash Table}).
-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.
+You don't strictly need a new data structure for this. You could
+instead modify the code in @file{userprog/pagedir.c}. If you do that
+you'll need to thoroughly understand how 80@var{x}86 page tables work
+by, e.g.,@: studying section 3.7, ``Page Translation Using 32-Bit
+Physical Addressing,'' in @bibref{IA32-v3a}. In practice, most groups
+use a separate data structure.
@item
Some way of finding a page on disk (in a file or in swap) if it is not
perform at least as well as the ``second chance'' or ``clock''
algorithm.
-Your design should allow for parallelism. Multiple processes should
-be able to process page faults at once. If one page fault require
+Your design should allow for parallelism. If one page fault requires
I/O, in the meantime processes that do not fault should continue
-executing and other page faults that do not require I/O should be able to
-complete. These criteria require some synchronization effort.
+executing and other page faults that do not require I/O should be able
+to complete. These criteria require some synchronization effort.
@node Lazy Loading
@subsection Lazy Loading
The core of the program loader is the loop in @func{load_segment} in
@file{userprog/process.c}.
-Each time around the loop, @code{read_bytes} receives the number of
-bytes to read from the executable file and @code{zero_bytes} receives
+Each time around the loop, @code{page_read_bytes} receives the number of
+bytes to read from the executable file and @code{page_zero_bytes} receives
the number of bytes to initialize to zero following the bytes read. The
two always sum to @code{PGSIZE} (4,096). The handling of a page depends
on these variables' values:
@itemize @bullet
@item
-If @code{read_bytes} equals @code{PGSIZE}, the page should be demand
+If @code{page_read_bytes} equals @code{PGSIZE}, the page should be demand
paged from disk on its first access.
@item
-If @code{zero_bytes} equals @code{PGSIZE}, the page does not need to
+If @code{page_zero_bytes} equals @code{PGSIZE}, the page does not need to
be read from disk at all because it is all zeroes. You should handle
such pages by creating a new page consisting of all zeroes at the
first page fault.
@item
-If neither @code{read_bytes} nor @code{zero_bytes} equals
+If neither @code{page_read_bytes} nor @code{page_zero_bytes} equals
@code{PGSIZE}, then part of the page is to be read from disk and the
remainder zeroed. This is a special case. You are allowed to handle
it by reading the partial page from disk at executable load time and
You can layer some other allocator on top of @func{palloc_get_page} if
you like, but it should be the underlying mechanism.
-Also, you can use the @option{-u} option to @command{pintos} to limit
+Also, you can use the @option{-ul} 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.
it like so:
@example
-write (addr, 64, STDOUT_FILENO);
+write (STDOUT_FILENO, addr, 64);
@end example
Similarly, if you wanted to replace the first byte of the file,
projects / pintos-anon / blobdiff