[PATCH v6 0/7] fs: implement multigrain timestamps

Jeff Layton
2023-07-25T14:58:55Z

The VFS always uses coarse-grained timestamps when updating the
ctime and mtime after a change. This has the benefit of allowing
filesystems to optimize away a lot metadata updates, down to around 1
per jiffy, even when a file is under heavy writes.

Unfortunately, this coarseness has always been an issue when we're
exporting via NFSv3, which relies on timestamps to validate caches. A
lot of changes can happen in a jiffy, so timestamps aren't sufficient to
help the client decide to invalidate the cache.

Even with NFSv4, a lot of exported filesystems don't properly support a
change attribute and are subject to the same problems with timestamp
granularity. Other applications have similar issues with timestamps (e.g
backup applications).

If we were to always use fine-grained timestamps, that would improve the
situation, but that becomes rather expensive, as the underlying
filesystem would have to log a lot more metadata updates.

What we need is a way to only use fine-grained timestamps when they are
being actively queried. The idea is to use an unused bit in the ctime's
tv_nsec field to mark when the mtime or ctime has been queried via
getattr. Once that has been marked, the next m/ctime update will use a
fine-grained timestamp.

This patch series is based on top of Christian's vfs.all branch, which
has the recent conversion to the new ctime accessors. It should apply
cleanly on top of linux-next.

The first two patches should probably go in via the vfs tree. Should the
fs-specific patches go in that way as well, or should they go via
maintainer trees? Either should be fine.

The first two patches should probably go in via Christian's vfs tree.
The rest could go via maintainer trees or the vfs tree.

For now, I'd like to get these into linux-next. Christian, would you be
willing to pick these up for now? Alternately, I can feed them there via
the iversion branch that Stephen is already pulling in from my tree.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
base-commit: cf22d118b89a09a0160586412160d89098f7c4c7
---
Changes in v6:
- drop the patch that removed XFS_ICHGTIME_CHG
- change WARN_ON_ONCE to ASSERT in xfs conversion patch

---
Jeff Layton (7):
fs: pass the request_mask to generic_fillattr
fs: add infrastructure for multigrain timestamps
tmpfs: bump the mtime/ctime/iversion when page becomes writeable
tmpfs: add support for multigrain timestamps
xfs: switch to multigrain timestamps
ext4: switch to multigrain timestamps
btrfs: convert to multigrain timestamps

fs/9p/vfs_inode.c | 4 +-
fs/9p/vfs_inode_dotl.c | 4 +-
fs/afs/inode.c | 2 +-
fs/btrfs/file.c | 24 ++--------
fs/btrfs/inode.c | 2 +-
fs/btrfs/super.c | 5 ++-
fs/ceph/inode.c | 2 +-
fs/coda/inode.c | 3 +-
fs/ecryptfs/inode.c | 5 ++-
fs/erofs/inode.c | 2 +-
fs/exfat/file.c | 2 +-
fs/ext2/inode.c | 2 +-
fs/ext4/inode.c | 2 +-
fs/ext4/super.c | 2 +-
fs/f2fs/file.c | 2 +-
fs/fat/file.c | 2 +-
fs/fuse/dir.c | 2 +-
fs/gfs2/inode.c | 2 +-
fs/hfsplus/inode.c | 2 +-
fs/inode.c | 98 +++++++++++++++++++++++++++++------------
fs/kernfs/inode.c | 2 +-
fs/libfs.c | 4 +-
fs/minix/inode.c | 2 +-
fs/nfs/inode.c | 2 +-
fs/nfs/namespace.c | 3 +-
fs/ntfs3/file.c | 2 +-
fs/ocfs2/file.c | 2 +-
fs/orangefs/inode.c | 2 +-
fs/proc/base.c | 4 +-
fs/proc/fd.c | 2 +-
fs/proc/generic.c | 2 +-
fs/proc/proc_net.c | 2 +-
fs/proc/proc_sysctl.c | 2 +-
fs/proc/root.c | 3 +-
fs/smb/client/inode.c | 2 +-
fs/smb/server/smb2pdu.c | 22 ++++-----
fs/smb/server/vfs.c | 3 +-
fs/stat.c | 59 ++++++++++++++++++++-----
fs/sysv/itree.c | 3 +-
fs/ubifs/dir.c | 2 +-
fs/udf/symlink.c | 2 +-
fs/vboxsf/utils.c | 2 +-
fs/xfs/libxfs/xfs_trans_inode.c | 6 +--
fs/xfs/xfs_iops.c | 4 +-
fs/xfs/xfs_super.c | 2 +-
include/linux/fs.h | 47 ++++++++++++++++++--
mm/shmem.c | 16 ++++++-
47 files changed, 248 insertions(+), 125 deletions(-)
---
base-commit: 810b5fff7917119ea82ff96e312e2d4350d6b681
change-id: 20230713-mgctime-f2a9fc324918

Best regards,
--
Jeff Layton <jlayton@kernel.org>