From 0f680ee8f2b6de9e4d07e1b1964899ef87c76f15 Mon Sep 17 00:00:00 2001 From: Zheng Liu Date: Sun, 13 Jan 2013 17:08:15 +0800 Subject: [PATCH] mke2fs: document bigalloc and cluster-size Bigalloc feature has been used for a long time, but the documentation in mke2fs is still missing. So add it. Addresses-Debian-Bug: #669730 Signed-off-by: Zheng Liu Signed-off-by: Theodore Ts'o --- misc/mke2fs.8.in | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in index d4fbe00..023ba49 100644 --- a/misc/mke2fs.8.in +++ b/misc/mke2fs.8.in @@ -187,6 +187,13 @@ Check the device for bad blocks before creating the file system. If this option is specified twice, then a slower read-write test is used instead of a fast read-only test. .TP +.B \-C " cluster-size" +Specify the size of cluster in bytes for filesystems using the bigalloc +feature. Valid cluster-size values are from 2048 to 256M bytes per +cluster. By default (if bigalloc is enabled and no cluster size is +otherwise specified using this option), the cluster size will be 16 +times the block size. +.TP .B \-D Use direct I/O when writing to the disk. This avoids mke2fs dirtying a lot of buffer cache memory, which may impact other applications running @@ -309,6 +316,10 @@ RAID parameter as part of the option rather than manipulating the number of blocks per group.) This option is generally used by developers who are developing test cases. +.IP +If the bigalloc feature is enabled, the +.B \-g +option will specify the number of clusters in a block group. .TP .BI \-G " number-of-groups" Specify the number of block groups that will be packed together to @@ -516,6 +527,21 @@ prefix the feature name with a caret ('^') character. The pseudo-filesystem feature "none" will clear all filesystem features. .RS 1.2i .TP +.B bigalloc +This feature enables clustered allocation, so that the unit of +allocation is a power of two number of blocks. That is, each bit in the +what had traditionally been known as the block allocation bitmap now +indicates whether a cluster is in use or not, where a cluster is by +default composed of 16 blocks. This feature can decrease the time +spent on doing block allocation and brings smaller fragmentation, especially +for large files. The size can be specified using the +.B \-C option. +.IP +.B Warning: +The bigalloc feature is still under development, and may not be fully +supported with your kernel or may have various bugs. Please see the web +page http://ext4.wiki.kernel.org/index.php/Bigalloc for details. +.TP .B dir_index Use hashed b-trees to speed up lookups in large directories. .TP -- 1.8.3.1