ext4: New inode/block allocation algorithms for flex_bg filesystems

The find_group_flex() inode allocator is now only used if the
filesystem is mounted using the "oldalloc" mount option.  It is
replaced with the original Orlov allocator that has been updated for
flex_bg filesystems (it should behave the same way if flex_bg is
disabled).  The inode allocator now functions by taking into account
each flex_bg group, instead of each block group, when deciding whether
or not it's time to allocate a new directory into a fresh flex_bg.

The block allocator has also been changed so that the first block
group in each flex_bg is preferred for use for storing directory
blocks.  This keeps directory blocks close together, which is good for
speeding up e2fsck since large directories are more likely to look
like this:

debugfs:  stat /home/tytso/Maildir/cur
Inode: 1844562   Type: directory    Mode:  0700   Flags: 0x81000
Generation: 1132745781    Version: 0x00000000:0000ad71
User: 15806   Group: 15806   Size: 1060864
File ACL: 0    Directory ACL: 0
Links: 2   Blockcount: 2072
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x499c0ff4:164961f4 -- Wed Feb 18 08:41:08 2009
 atime: 0x499c0ff4:00000000 -- Wed Feb 18 08:41:08 2009
 mtime: 0x49957f51:00000000 -- Fri Feb 13 09:10:25 2009
crtime: 0x499c0f57:00d51440 -- Wed Feb 18 08:38:31 2009
Size of extra inode fields: 28
BLOCKS:
(0):7348651, (1-258):7348654-7348911
TOTAL: 259

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 24 insertions, 1 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e0aa4fe4f59..aa3431856c9 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -152,6 +152,8 @@ static ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
 	ext4_fsblk_t bg_start;
 	ext4_fsblk_t last_block;
 	ext4_grpblk_t colour;
+	ext4_group_t block_group;
+	int flex_size = ext4_flex_bg_size(EXT4_SB(inode->i_sb));
 	int depth;
 
 	if (path) {
@@ -170,10 +172,31 @@ static ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
 	}
 
 	/* OK. use inode's group */
-	bg_start = (ei->i_block_group * EXT4_BLOCKS_PER_GROUP(inode->i_sb)) +
+	block_group = ei->i_block_group;
+	if (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) {
+		/*
+		 * If there are at least EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME
+		 * block groups per flexgroup, reserve the first block 
+		 * group for directories and special files.  Regular 
+		 * files will start at the second block group.  This
+		 * tends to speed up directory access and improves 
+		 * fsck times.
+		 */
+		block_group &= ~(flex_size-1);
+		if (S_ISREG(inode->i_mode))
+			block_group++;
+	}
+	bg_start = (block_group * EXT4_BLOCKS_PER_GROUP(inode->i_sb)) +
 		le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_first_data_block);
 	last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;
 
+	/*
+	 * If we are doing delayed allocation, we don't need take
+	 * colour into account.
+	 */
+	if (test_opt(inode->i_sb, DELALLOC))
+		return bg_start;
+
 	if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
 		colour = (current->pid % 16) *
 			(EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);