On Tue, May 15, 2012 at 05:00:29PM -0400, J. Bruce Fields wrote: > On Tue, May 15, 2012 at 04:05:34PM -0400, Josef Bacik wrote: > > On Tue, May 15, 2012 at 01:55:33PM -0600, Andreas Dilger wrote: > > > It should be fairly straight forward to have a flag set in the ext4 > > > superblock (s_state flag?) that indicates that the filesystem has > > > been exported via NFS. There might be other optimizations that can > > > be done based on this (e.g. avoid some of the directory cookie > > > hijinx that are only needed if NFS has exported the filesystem and > > > needs to keep persistent cookies across reboots). > > > > > > I think that the ext4_mark_inode_dirty() performance problem could > > > be at least partially fixed by deferring the copy of in-core inode > > > to on-disk inode to use a journal commit callback. This is far more > > > work than just setting a flag in the superblock, but it has the > > > potential to _improve_ performance rather than make it worse. > > Could you give any more pointers for an ext4 ignoramus? (Where *is* the > journal commit code that would need the callback? And where is the copy > currently done?) > The copy is currently done in mark_inode_dirty(), I'm looking into what would need to be done to get the inodes to update the on disk stuff on journal commit only, but I worry that will make commits take way longer than normal and cause other issues. > > Yeah Btrfs doesn't have this sort of problem since we delay inode > > updating sinc it is so costly, we simply let it hang around in the > > in-core inode until we feel like updating it at some point down the > > road. I'll put together a feature flag or something to make it be > > enabled for always if somebody turns it on. > > Thanks for looking at this. > > A feature flag would be an improvement over a mount option. > > If the flag makes a noticeable difference to performance, then it makes > me nervous toggling it automatically. And what will we do if statx > starts returning i_version to userspace? > Well statx can return flags right? I'm sure we could just have a flag that says "hey iversion is completely useless." Thanks, Josef -- 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
