Re: [PATCH 5/9] fuse: cache atime when in iomap mode

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Apr 29, 2026 at 07:34:22AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> When we're running in iomap mode, allow the kernel to cache the access
> timestamp to further reduce the number of roundtrips to the fuse server.
> 
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
>  fs/fuse/dir.c        |    5 +++++
>  fs/fuse/fuse_iomap.c |    6 ++++++
>  fs/fuse/inode.c      |   11 ++++++++---
>  3 files changed, 19 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 53fda7f63b11c8..61015e83888ee4 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -2236,6 +2236,11 @@ int fuse_flush_times(struct inode *inode, struct fuse_file *ff)
>  		inarg.ctime = inode_get_ctime_sec(inode);
>  		inarg.ctimensec = inode_get_ctime_nsec(inode);
>  	}
> +	if (fuse_inode_has_iomap(inode)) {
> +		inarg.valid |= FATTR_ATIME;
> +		inarg.atime = inode_get_atime_sec(inode);
> +		inarg.atimensec = inode_get_atime_nsec(inode);
> +	}
>  	if (ff) {
>  		inarg.valid |= FATTR_FH;
>  		inarg.fh = ff->fh;
> diff --git a/fs/fuse/fuse_iomap.c b/fs/fuse/fuse_iomap.c
> index a39370b97ca508..9278e2e399ba9b 100644
> --- a/fs/fuse/fuse_iomap.c
> +++ b/fs/fuse/fuse_iomap.c
> @@ -1169,6 +1169,12 @@ void fuse_iomap_init_inode(struct inode *inode, struct fuse_attr *attr)
>  	if (attr->flags & FUSE_ATTR_ATOMIC)
>  		fuse_inode_set_atomic(inode);
>  
> +	/*
> +	 * iomap caches atime too, so we must load it from the fuse server
> +	 * at instantiation time.
> +	 */
> +	inode_set_atime(inode, attr->atime, attr->atimensec);
> +
>  	trace_fuse_iomap_init_inode(inode);
>  }
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index aa9f880b9a2ea6..1a09b9e1446919 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -266,7 +266,8 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
>  	attr->mtimensec = min_t(u32, attr->mtimensec, NSEC_PER_SEC - 1);
>  	attr->ctimensec = min_t(u32, attr->ctimensec, NSEC_PER_SEC - 1);
>  
> -	inode_set_atime(inode, attr->atime, attr->atimensec);
> +	if (!(cache_mask & STATX_ATIME))
> +		inode_set_atime(inode, attr->atime, attr->atimensec);
>  	/* mtime from server may be stale due to local buffered write */
>  	if (!(cache_mask & STATX_MTIME)) {
>  		inode_set_mtime(inode, attr->mtime, attr->mtimensec);
> @@ -331,8 +332,12 @@ u32 fuse_get_cache_mask(struct inode *inode)
>  {
>  	struct fuse_conn *fc = get_fuse_conn(inode);
>  
> -	if (S_ISREG(inode->i_mode) &&
> -	    (fuse_inode_has_iomap(inode) || fc->writeback_cache))
> +	if (!S_ISREG(inode->i_mode))
> +		return 0;
> +
> +	if (fuse_inode_has_iomap(inode))
> +		return STATX_MTIME | STATX_CTIME | STATX_ATIME | STATX_SIZE;
> +	if (fc->writeback_cache)

Every once in a blue moon I noticed that the atime falls behind the
ondisk ext4 filesystem in the stat output.  I *think* this is a result
of fuse_change_attributes_i not overwriting the supplied attr->atime
with whatever's in the inode.  I'll change that, and let's see if the
periodic fstests complaints go away.

--D

>  		return STATX_MTIME | STATX_CTIME | STATX_SIZE;
>  
>  	return 0;
> 
>