1 files changed, 75 insertions, 50 deletions

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 0c5086db8352..80e193d82e2e 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -13,72 +13,93 @@ Mailing list: linux-ext4@vger.kernel.org
 1. Quick usage instructions:
 ===========================
 
-  - Grab updated e2fsprogs from
-    ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs-interim/
-    This is a patchset on top of e2fsprogs-1.39, which can be found at
+  - Compile and install the latest version of e2fsprogs (as of this
+    writing version 1.41) from:
+
+    http://sourceforge.net/project/showfiles.php?group_id=2406
+        
+        or
+
     ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
 
-  - It's still mke2fs -j /dev/hda1
+        or grab the latest git repository from:
+
+    git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
+
+  - Create a new filesystem using the ext4dev filesystem type:
+
+        # mke2fs -t ext4dev /dev/hda1
+
+    Or configure an existing ext3 filesystem to support extents and set
+    the test_fs flag to indicate that it's ok for an in-development
+    filesystem to touch this filesystem:
 
-  - mount /dev/hda1 /wherever -t ext4dev
+        # tune2fs -O extents -E test_fs /dev/hda1
 
-  - To enable extents,
+    If the filesystem was created with 128 byte inodes, it can be
+    converted to use 256 byte for greater efficiency via:
 
-        mount /dev/hda1 /wherever -t ext4dev -o extents
+        # tune2fs -I 256 /dev/hda1
 
-  - The filesystem is compatible with the ext3 driver until you add a file
-    which has extents (ie: `mount -o extents', then create a file).
+    (Note: we currently do not have tools to convert an ext4dev
+    filesystem back to ext3; so please do not do try this on production
+    filesystems.)
 
-    NOTE: The "extents" mount flag is temporary.  It will soon go away and
-    extents will be enabled by the "-o extents" flag to mke2fs or tune2fs
+  - Mounting:
+
+        # mount -t ext4dev /dev/hda1 /wherever
 
   - When comparing performance with other filesystems, remember that
-    ext3/4 by default offers higher data integrity guarantees than most.  So
-    when comparing with a metadata-only journalling filesystem, use `mount -o
-    data=writeback'.  And you might as well use `mount -o nobh' too along
-    with it.  Making the journal larger than the mke2fs default often helps
-    performance with metadata-intensive workloads.
+    ext3/4 by default offers higher data integrity guarantees than most.
+    So when comparing with a metadata-only journalling filesystem, such
+    as ext3, use `mount -o data=writeback'.  And you might as well use
+    `mount -o nobh' too along with it.  Making the journal larger than
+    the mke2fs default often helps performance with metadata-intensive
+    workloads.
 
 2. Features
 ===========
 
 2.1 Currently available
 
-* ability to use filesystems > 16TB
+* ability to use filesystems > 16TB (e2fsprogs support not available yet)
 * extent format reduces metadata overhead (RAM, IO for access, transactions)
 * extent format more robust in face of on-disk corruption due to magics,
 * internal redunancy in tree
-
-2.1 Previously available, soon to be enabled by default by "mkefs.ext4":
-
-* dir_index and resize inode will be on by default
-* large inodes will be used by default for fast EAs, nsec timestamps, etc
+* improved file allocation (multi-block alloc)
+* fix 32000 subdirectory limit
+* nsec timestamps for mtime, atime, ctime, create time
+* inode version field on disk (NFSv4, Lustre)
+* reduced e2fsck time via uninit_bg feature
+* journal checksumming for robustness, performance
+* persistent file preallocation (e.g for streaming media, databases)
+* ability to pack bitmaps and inode tables into larger virtual groups via the
+  flex_bg feature
+* large file support
+* Inode allocation using large virtual block groups via flex_bg
+* delayed allocation
+* large block (up to pagesize) support
+* efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force
+  the ordering)
 
 2.2 Candidate features for future inclusion
 
-There are several under discussion, whether they all make it in is
-partly a function of how much time everyone has to work on them:
+* Online defrag (patches available but not well tested)
+* reduced mke2fs time via lazy itable initialization in conjuction with
+  the uninit_bg feature (capability to do this is available in e2fsprogs
+  but a kernel thread to do lazy zeroing of unused inode table blocks
+  after filesystem is first mounted is required for safety)
 
-* improved file allocation (multi-block alloc, delayed alloc; basically done)
-* fix 32000 subdirectory limit (patch exists, needs some e2fsck work)
-* nsec timestamps for mtime, atime, ctime, create time (patch exists,
-  needs some e2fsck work)
-* inode version field on disk (NFSv4, Lustre; prototype exists)
-* reduced mke2fs/e2fsck time via uninitialized groups (prototype exists)
-* journal checksumming for robustness, performance (prototype exists)
-* persistent file preallocation (e.g for streaming media, databases)
+There are several others under discussion, whether they all make it in is
+partly a function of how much time everyone has to work on them. Features like
+metadata checksumming have been discussed and planned for a bit but no patches
+exist yet so I'm not sure they're in the near-term roadmap.
 
-Features like metadata checksumming have been discussed and planned for
-a bit but no patches exist yet so I'm not sure they're in the near-term
-roadmap.
+The big performance win will come with mballoc, delalloc and flex_bg
+grouping of bitmaps and inode tables.  Some test results available here:
 
-The big performance win will come with mballoc and delalloc.  CFS has
-been using mballoc for a few years already with Lustre, and IBM + Bull
-did a lot of benchmarking on it.  The reason it isn't in the first set of
-patches is partly a manageability issue, and partly because it doesn't
-directly affect the on-disk format (outside of much better allocation)
-so it isn't critical to get into the first round of changes.  I believe
-Alex is working on a new set of patches right now.
+ - http://www.bullopensource.org/ext4/20080530/ffsb-write-2.6.26-rc2.html
+ - http://www.bullopensource.org/ext4/20080530/ffsb-readwrite-2.6.26-rc2.html
 
 3. Options
 ==========
@@ -222,9 +243,11 @@ stripe=n		Number of filesystem blocks that mballoc will try
                         to use for allocation size and alignment. For RAID5/6
                         systems this should be the number of data
                         disks *  RAID chunk size in file system blocks.
-
+delalloc        (*)     Deferring block allocation until write-out time.
+nodelalloc              Disable delayed allocation. Blocks are allocation
+                        when data is copied from user to page cache.
 Data Mode
----------
+=========
 There are 3 different data modes:
 
 * writeback mode
@@ -236,10 +259,10 @@ typically provide the best ext4 performance.
 
 * ordered mode
 In data=ordered mode, ext4 only officially journals metadata, but it logically
-groups metadata and data blocks into a single unit called a transaction.  When
-it's time to write the new metadata out to disk, the associated data blocks
-are written first.  In general, this mode performs slightly slower than
-writeback but significantly faster than journal mode.
+groups metadata information related to data changes with the data blocks into a
+single unit called a transaction.  When it's time to write the new metadata
+out to disk, the associated data blocks are written first.  In general,
+this mode performs slightly slower than writeback but significantly faster than journal mode.
 
 * journal mode
 data=journal mode provides full data and metadata journaling.  All new data is
@@ -247,7 +270,8 @@ written to the journal first, and then to its final location.
 In the event of a crash, the journal can be replayed, bringing both data and
 metadata into a consistent state.  This mode is the slowest except when data
 needs to be read from and written to disk at the same time where it
-outperforms all others modes.
+outperforms all others modes.  Curently ext4 does not have delayed
+allocation support if this data journalling mode is selected.
 
 References
 ==========
@@ -256,7 +280,8 @@ kernel source:	<file:fs/ext4/>
                 <file:fs/jbd2/>
 
 programs:       http://e2fsprogs.sourceforge.net/
-                http://ext2resize.sourceforge.net
 
 useful links:   http://fedoraproject.org/wiki/ext3-devel
                 http://www.bullopensource.org/ext4/
+                http://ext4.wiki.kernel.org/index.php/Main_Page
+                http://fedoraproject.org/wiki/Features/Ext4