Explain better what we expect from the buffer cache.

[pintos-anon] / doc / filesys.texi

diff --git a/doc/filesys.texi b/doc/filesys.texi
index db4d94810b63426f91ee03c6783bd63b5c1060be..1b666b3b6e3ca24dbc3c1579ee3c8df4b10b934f 100644 (file)
--- a/doc/filesys.texi
+++ b/doc/filesys.texi
@@ -96,9 +96,9 @@ system.
 The grading scripts check the file system's correctness based on the
 contents of the file copied out in the second run.  This means that your
 project will not pass any of the extended file system tests until the
-file system is implemented well enough to support @program{tar}, the
+file system is implemented well enough to support @command{tar}, the
 Pintos user program that produces the file that is copied out.  The
-@program{tar} program is fairly demanding (it requires both extensible
+@command{tar} program is fairly demanding (it requires both extensible
 file and subdirectory support), so this will take some work.  Until
 then, you can ignore errors from @command{make check} regarding the
 extracted file system.
@@ -259,8 +259,8 @@ false if it represents an ordinary file.
 @end deftypefn
 
 @deftypefn {System Call} int inumber (int @var{fd})
-Returns the @dfn{inode number} of the inode associated with @var{fd}.
-Applicable to file descriptors for both files and directories.
+Returns the @dfn{inode number} of the inode associated with @var{fd},
+which may represent an ordinary file or a directory.
 
 An inode number persistently identifies a file or directory.  It is
 unique during the file's existence.  In Pintos, the sector number of the
@@ -287,11 +287,12 @@ disk.  Otherwise, fetch the block from disk into cache, evicting an
 older entry if necessary.  You are limited to a cache no greater than 64
 sectors in size.
 
-Be sure to choose an intelligent cache replacement algorithm.
-Experiment to see what combination of accessed, dirty, and other
-information results in the best performance, as measured by the number
-of disk accesses.  For example, metadata is generally more valuable to
-cache than data.
+You must implement a cache replacement algorithm that is at least as
+good as the ``clock'' algorithm.  Your algorithm must also account for
+the generally greater value of metadata compared to data.  Experiment
+to see what combination of accessed, dirty, and other information
+results in the best performance, as measured by the number of disk
+accesses.
 
 You can keep a cached copy of the free map permanently in memory if you
 like.  It doesn't have to count against the cache size.
@@ -311,11 +312,8 @@ blocks back to disk.  The cache should also be written back to disk in
 @func{filesys_done}, so that halting Pintos flushes the cache.
 
 If you have @func{timer_sleep} from the first project working, write-behind is
-an excellent application.  If you're still using the base
-implementation of @func{timer_sleep}, be aware that it busy-waits, which
-is not acceptable here (or elsewhere).  If @func{timer_sleep}'s delays seem too
-short or too long, reread the explanation of the @option{-r} option to
-@command{pintos} (@pxref{Debugging versus Testing}).
+an excellent application.  Otherwise, you may implement a less general
+facility, but make sure that it does not exhibit busy-waiting.
 
 You should also implement @dfn{read-ahead}, that is,
 automatically fetch the next block of a file