2 files changed, 23 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4
index f22ac0872ae8..c631253cf85c 100644
--- a/Documentation/ABI/testing/sysfs-fs-ext4
+++ b/Documentation/ABI/testing/sysfs-fs-ext4
@@ -96,3 +96,16 @@ Contact:	"Theodore Ts'o" <tytso@mit.edu>
 Description:
                 The maximum number of megabytes the writeback code will
                 try to write out before move on to another inode.
+
+What:           /sys/fs/ext4/<disk>/extent_max_zeroout_kb
+Date:           August 2012
+Contact:        "Theodore Ts'o" <tytso@mit.edu>
+Description:
+                The maximum number of kilobytes which will be zeroed
+                out in preference to creating a new uninitialized
+                extent when manipulating an inode's extent tree.  Note
+                that using a larger value will increase the
+                variability of time necessary to complete a random
+                write operation (since a 4k random write might turn
+                into a much larger write due to the zeroout
+                operation).
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 1b7f9acbcbbe..104322bf378c 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -375,6 +375,16 @@ dioread_nolock		locking. If the dioread_nolock option is specified
                         Because of the restrictions this options comprises
                         it is off by default (e.g. dioread_lock).
 
+max_dir_size_kb=n       This limits the size of directories so that any
+                        attempt to expand them beyond the specified
+                        limit in kilobytes will cause an ENOSPC error.
+                        This is useful in memory constrained
+                        environments, where a very large directory can
+                        cause severe performance problems or even
+                        provoke the Out Of Memory killer.  (For example,
+                        if there is only 512mb memory available, a 176mb
+                        directory may seriously cramp the system's style.)
+
 i_version               Enable 64-bit inode version support. This option is
                         off by default.