Re: [PATCH 11/14] fs: add a ->sync_lazytime method

Chaitanya Kulkarni
2025-11-17T07:50:42Z

On 11/13/25 22:26, Christoph Hellwig wrote:
> Allow the file system to explicitly implement lazytime syncing instead
> of pigging back on generic inode dirtying. This allows to simplify
> the XFS implementation and prepares for non-blocking lazytime timestamp
> updates.
>
> Signed-off-by: Christoph Hellwig<hch@lst.de>
> ---
> Documentation/filesystems/locking.rst | 2 ++
> Documentation/filesystems/vfs.rst | 6 ++++++
> fs/fs-writeback.c | 13 +++++++++++--
> include/linux/fs.h | 1 +
> 4 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
> index 77704fde9845..9b2f14ada8cd 100644
> --- a/Documentation/filesystems/locking.rst
> +++ b/Documentation/filesystems/locking.rst
> @@ -81,6 +81,7 @@ prototypes::
> ssize_t (*listxattr) (struct dentry *, char *, size_t);
> int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
> void (*update_time)(struct inode *, struct timespec *, int);
> + void (*sync_lazytime)(struct inode *inode);
> int (*atomic_open)(struct inode *, struct dentry *,
> struct file *, unsigned open_flag,
> umode_t create_mode);
> @@ -117,6 +118,7 @@ getattr: no
> listxattr: no
> fiemap: no
> update_time: no
> +sync_lazytime: no
> atomic_open: shared (exclusive if O_CREAT is set in open flags)
> tmpfile: no
> fileattr_get: no or exclusive
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index 4f13b01e42eb..ff59760daae2 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -486,6 +486,7 @@ As of kernel 2.6.22, the following members are defined:
> int (*getattr) (struct mnt_idmap *, const struct path *, struct kstat *, u32, unsigned int);
> ssize_t (*listxattr) (struct dentry *, char *, size_t);
> void (*update_time)(struct inode *, struct timespec *, int);
> + void (*sync_lazytime)(struct inode *inode);
> int (*atomic_open)(struct inode *, struct dentry *, struct file *,
> unsigned open_flag, umode_t create_mode);
> int (*tmpfile) (struct mnt_idmap *, struct inode *, struct file *, umode_t);
> @@ -642,6 +643,11 @@ otherwise noted.
> an inode. If this is not defined the VFS will update the inode
> itself and call mark_inode_dirty_sync.
>
> +``sync_lazytime``:
> + called by the writeback code to update the lazy time stamps to
> + regular time stamp updates that get syncing into the on-disk
> + inode.
> +
> ``atomic_open``
> called on the last component of an open. Using this optional
> method the filesystem can look up, possibly create and open the
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index ae6d1f1ccc71..7245f547416f 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1699,7 +1699,10 @@ bool sync_lazytime(struct inode *inode)
> return false;
>
> trace_writeback_lazytime(inode);
> - mark_inode_dirty_sync(inode);
> + if (inode->i_op->sync_lazytime)
> + inode->i_op->sync_lazytime(inode);
> + else
> + mark_inode_dirty_sync(inode);
> return false;
> }
>
> @@ -2547,6 +2550,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> trace_writeback_mark_inode_dirty(inode, flags);
>
> if (flags & I_DIRTY_INODE) {
> + bool was_dirty_time = true;
> +
> /*
> * Inode timestamp update will piggback on this dirtying.
> * We tell ->dirty_inode callback that timestamps need to
> @@ -2557,6 +2562,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> if (inode->i_state & I_DIRTY_TIME) {
> inode->i_state &= ~I_DIRTY_TIME;
> flags |= I_DIRTY_TIME;
> + was_dirty_time = true;
> }
> spin_unlock(&inode->i_lock);
> }

was_dirty_time is initialized it to true and above true again,
perhaps it should be initialized it to false, so it will be only set to
true when inode->i_state &= I_DIRTY_TIME; ?

if was_dirty_time always set to true at the time of initialization then
below check will always call as long as callback is set
inode->i_op->sync_lazytime(), irrespective of
inode->i_state &= I_DIRTY_TIME; assignment.

-ck