On Thu, Nov 27, 2014 at 03:27:31PM -0500, Theodore Ts'o wrote: > I can do that, but part of the reason why we were doing this rather > involved set of changes was to allow other file systems to be able to > take advantage of lazytime. I suppose there is value in allowing > other file systems, such as jfs, f2fs, etc., to use it, but still, > it's a bit of a shame to drop btrfs and xfs support for this feature. I want to see xfs and btrfs support, but I think we're running in some conceptual problems here. I don't have the time right now to fully review the XFS changes for correctness and test them, and I'd rather keep things as-is for a while and then add properly designed and fully teste support in rather than something possible broken. > I'll note by the way that ext3 and ext4 doesn't really use VFS dirty > tracking either --- see my other comments about the naming of > "mark_inode_dirty" being a bit misleading, at least for all/most of > the major file systems. The problem seems to be that replacement > schemes that we've all using are slightly different. :-/ Indeed. It seems all existing ->dirty_inode instances basically just try to work around the problem that the VFS simply updates timestamps by writing into the inode without involving the filesystem. There are all kinds of bugs in different instances, as well as comments mentioning an assumption that this only happens for atime although the VFS also dos this "trick" for c/mtime, including a caller from the page fault code that the filesystems can't even avoid by providing non-default methods everywhere. > I suppose should let the btrfs folks decide whether they want to add > is_readonly() and write_time() function --- or maybe help with the > cleanup work so that mark_inode_dirty() can reflect an error to its > callers. Chris, David, what do you think? The ->is_readonly method seems like a clear winner to me, I'm all for adding it, and thus suggested moving it first in the series. I've read a bit more through the series and would like to suggest the following approach for the rest: - convert ext3/4 to use ->update_time instead of the ->dirty_time callout so it gets and exact notifications (preferably the few remaining filesystems as well, although that shouldn't really be a blocker) - defer timestamp updates for any filesystems not defining ->update_time (or ->dirty_time for now), and allow filesystems using ->update_time to defer the update as well by calling mark_inode_dirty with the I_DIRTY_TIME flag so that XFS and btrfs don't have to opt-in without testing. - Convert xfs, btrfs and the remaining filesystes using ->dirty_inode incrementally. -- 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
