At LSF/MM this year, we had a discussion about the inode change attribute. At the time I mentioned that I thought I could salvage the multigrain timestamp work that had to be reverted last year [1]. That version had to be reverted because it was possible for a file to get a coarse grained timestamp that appeared to be earlier than another file that had recently gotten a fine-grained stamp. This version corrects the problem by establishing a global ctime_floor value that should prevent this from occurring. In the above situation that was problematic before, the two files might end up with the same timestamp value, but they won't appear to have been modified in the wrong order. That problem was discovered by the test-stat-time gnulib test. Note that that test still fails on multigrain timestamps, but that's because its method of determining the minimum delay that will show a timestamp change will no longer work with multigrain timestamps. I have a patch to change the testcase to use a different method that I will post soon. The big question with this set is whether the performance will be suitable. The testing I've done seems to show performance parity with multigrain timestamps enabled, but it's hard to rule this out regressing some workload. This set is based on top of Christian's vfs.misc branch (which has the earlier change to track inode timestamps as discrete integers). If there are no major objections, I'd like to let this soak in linux-next for a bit to see if any problems shake out. [1]: https://lore.kernel.org/linux-fsdevel/20230807-mgctime-v7-0-d1dec143a704@xxxxxxxxxx/ Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> --- Jeff Layton (10): fs: turn inode ctime fields into a single ktime_t fs: uninline inode_get_ctime and inode_set_ctime_to_ts fs: tracepoints for inode_needs_update_time and inode_set_ctime_to_ts fs: add infrastructure for multigrain timestamps fs: add percpu counters to count fine vs. coarse timestamps fs: have setattr_copy handle multigrain timestamps appropriately xfs: switch to multigrain timestamps ext4: switch to multigrain timestamps btrfs: convert to multigrain timestamps tmpfs: add support for multigrain timestamps fs/attr.c | 52 +++++++-- fs/btrfs/file.c | 25 +---- fs/btrfs/super.c | 3 +- fs/ext4/super.c | 2 +- fs/inode.c | 222 +++++++++++++++++++++++++++++++++++---- fs/stat.c | 39 ++++++- fs/xfs/libxfs/xfs_trans_inode.c | 6 +- fs/xfs/xfs_iops.c | 6 +- fs/xfs/xfs_super.c | 2 +- include/linux/fs.h | 61 +++++++---- include/trace/events/timestamp.h | 173 ++++++++++++++++++++++++++++++ mm/shmem.c | 2 +- 12 files changed, 514 insertions(+), 79 deletions(-) --- base-commit: 33b321ac3a51e590225585f41c7412b86e987a0d change-id: 20240626-mgtime-5cd80b18d810 Best regards, -- Jeff Layton <jlayton@xxxxxxxxxx>
