On Wed, Aug 27, 2008 at 07:36:07PM +0200, Frédéric Bohé wrote: > While playing with filesystems using flex bg, I noticed that the journal > file may be fragmented when there are a lots of meta-data in the first > flex-group. > For example, with this command : mkfs.ext4 -t ext4dev -G512 /dev/sdb1 > The journal file is reported by "stat <8>" in debugfs to be like this : Yeah, we really want to put the journal in the middle of the filesystem; that not only avoids the metadata at the very beginning of the filesystem, especially when flex_bg is enabled, but also because it eliminates the worst case seek times when the file data is at the end of the disk, and the journal is at the beginning of the disk, and we are using a very fsync-intensive workload. With the following patches the journal inode now looks like this: Inode: 8 Type: regular Mode: 0600 Flags: 0x80000 Generation: 0 Version: 0x00000000 User: 0 Group: 0 Size: 134217728 File ACL: 0 Directory ACL: 0 Links: 1 Blockcount: 262144 Fragment: Address: 0 Number: 0 Size: 0 ctime: 0x48b5b982 -- Wed Aug 27 16:30:58 2008 atime: 0x00000000 -- Wed Dec 31 19:00:00 1969 mtime: 0x48b5b982 -- Wed Aug 27 16:30:58 2008 Size of extra inode fields: 0 BLOCKS: (0-32767):2588672-2621439 TOTAL: 32768 This also creates the journal using extents, which eliminates the indirect block overhead, and means that the 128MB journal conveniently takes up a single block group: Group 79: (Blocks 2588672-2621439) [INODE_UNINIT, ITABLE_ZEROED] Checksum 0x441d, unused inodes 8192 Block bitmap at 2097167, Inode bitmap at 2097183 Inode table at 2104864-2105375 0 free blocks, 8192 free inodes, 0 directories, 8192 unused inodes Free blocks: Free inodes: - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
