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Ext4 Developer Interlock Call: 12-13-06 Minutes

Attendees: Mingming Cao, Dave Kleikamp, Takashi Sato, Suparna Bhattacharya, Jean-Pierre Dion, Jean-Noel Cordenner, Valérie Clément, Ted Ts'o, Avantika Mathur
Minutes can be accessed at: http://ext4.wiki.kernel.org/index.php/Ext4_Developer%27s_Conference_Call

  • Conferences:
    • The Linux filesystem and storage workshop is coming up in February
    • OLS: deadline to submit abstracts is Feb 1st. Ted is thinking about a paper on e2fsprogs. Encouraging writing in-depth technical papers on ext4 work.
  • Ted will set up a git tree on kernel.org with all of the ext4 patches; so it is easy to access and test all of the patch sets.
  • Mingming will send an email requesting everyone to resend latest versions of ext4 patches to the mailing list, with a short description and status including 'to dos' and outstanding issues.

Ext4 Roadmap - an update on ext4 features in progress
These updates will also be added to the wiki page: http://ext4.wiki.kernel.org/index.php/New_ext4_features

  • Multiple Block Allocation
    • status: Patches are available and there are no format or e2fsprogs changes. given that there are no dependencies, this feature should be pushed to mainline soon.
    • outstanding issues: none
  • Delayed Allocation
    • status: Patches are available, and have been commented on -- need more work.
    • outstanding issues: lack of plan for 1k,2k block size and default data=order mode, and Andrew asked for more comments.
  • Preallocation
    • status: Kernel implementation and e2fsprogs changes are complete, and have been thoroughly reviewed by Mingming and Alex Tomas.
    • outstanding issues: Need consensus on what interface should be used (ioctl, fcntl..). What should the return value be on success, zero or number of block allocated. Suparna will post a comment for a case where the extent is allocated far off on the disk. Once the interface is decided, this feature will be ready to add to the git tree.
    • Andrew Morton has mentioned adding preallocation to directories. Ted and Mingming discussed adding readahead and reservation to directories rather than better than preallocatin.
  • Online Defragmentation:
    • status: Takashi sent updated patches last month. He will repost most recent version to the list.
    • outstanding issues: unknown
  • Break 32000 directory limit:
    • status: Andreas Dilger posted this patch. It is a simple patch with minor e2fsrogs changes. Ask Andreas to repost patches on ext4.
    • outstanding issues: unknown
  • Nanosecond Timestamps
    • status: Patches have been posted by Andreas Dilger, shouldn't need much rework once issues are resolved.
    • outstanding issues: Should be available in 128 bit inodes, or only in larger inodes. What effect updating the nanosecond timestamp has on performance, excessive atime updates. Should atime be kept at ~1 second granularity.
  • Change Attribute
    • status: use i_version rather than change_attribute field for this feature. Jean-Noel will resend out latest patch with summary and status
    • outstanding issues: unknown
  • Uninitialized Groups
    • status: Feature will reduce fsck time on a large filesystem. Currently this features is very premature and in prototype mode. Basic functionality for testing on 64 bit is in place, but not yet useful in production. There are no dependencies on this feature, for safety the feature depnds on checksumming block groups. Ask Andreas to resend patches.
    • outstanding issues: prototype mode
  • Journal Checksumming
    • status: feature will speed up journaling. The feature was proposed, but there is no status on patches.
    • outstanding issues: n/a
  • Undelete Feature for Ext4
    • status: Idea was proposed on the mailing list, still need more thought on the feature.
    • outstanding issues: Should the kernel be involved with undelete
  • Large file support
    • status: Increase 2Tb limit on filesize. Takashi has begun working on this.
    • outstanding issues: unknown

  • E2fsprogs work
    • Ted is working on a user issue handling > 375 million directories on a 32 bit machine
    • Correct interfaces for extents
    • adding 64 bit API without causing ABI breakages. Might need a major version change with the ABI breakage.
  • Supporting Trillions of Files in Ext4
    • Mingming and Avantika are looking into this
    • Issues and Constraints: difficult to support more than 32 bits of inodes, filsystem format and compatibility issues, stat interface is only 32 bits, memory utilization of inode cache will affect performance
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