[Virtio-fs] [PATCH v6 6/7] fuse: mark inode DONT_CACHE when per-file DAX hint changes

[Vivek Goyal]

On Mon, Oct 11, 2021 at 11:00:51AM +0800, Jeffle Xu wrote:
> When the per-file DAX hint changes while the file is still *opened*, it
> is quite complicated and maybe fragile to dynamically change the DAX
> state.
> 
> Hence mark the inode and corresponding dentries as DONE_CACHE once the
> per-file DAX hint changes, so that the inode instance will be evicted
> and freed as soon as possible once the file is closed and the last
> reference to the inode is put. And then when the file gets reopened next
> time, the new instantiated inode will reflect the new DAX state.
> 
> In summary, when the per-file DAX hint changes for an *opened* file, the
> DAX state of the file won't be updated until this file is closed and
> reopened later.
> 
> Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
> ---
>  fs/fuse/dax.c    | 9 +++++++++
>  fs/fuse/fuse_i.h | 1 +
>  fs/fuse/inode.c  | 3 +++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index 15bde36829b8..ca083c13f5e8 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -1364,6 +1364,15 @@ void fuse_dax_inode_init(struct inode *inode, unsigned int flags)
>  	inode->i_data.a_ops = &fuse_dax_file_aops;
>  }
>  
> +void fuse_dax_dontcache(struct inode *inode, unsigned int flags)
> +{
> +	struct fuse_conn *fc = get_fuse_conn(inode);
> +
> +	if (fc->dax_mode == FUSE_DAX_INODE &&
> +	    (!!IS_DAX(inode) != !!(flags & FUSE_ATTR_DAX)))
> +		d_mark_dontcache(inode);
> +}
> +
>  bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment)
>  {
>  	if (fc->dax && (map_alignment > FUSE_DAX_SHIFT)) {
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 0270a41c31d7..bb2c11e0311a 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -1270,6 +1270,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc);
>  bool fuse_dax_inode_alloc(struct super_block *sb, struct fuse_inode *fi);
>  void fuse_dax_inode_init(struct inode *inode, unsigned int flags);
>  void fuse_dax_inode_cleanup(struct inode *inode);
> +void fuse_dax_dontcache(struct inode *inode, unsigned int flags);
>  bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment);
>  void fuse_dax_cancel_work(struct fuse_conn *fc);
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 73f19cd6e702..cf934c2ba761 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -268,6 +268,9 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
>  		if (inval)
>  			invalidate_inode_pages2(inode->i_mapping);
>  	}
> +
> +	if (IS_ENABLED(CONFIG_FUSE_DAX))
> +		fuse_dax_dontcache(inode, attr->flags);

Should we give this function more generic name. Say
fuse_dax_change_attributes(). And let that function decide what attributes
have changed and does it need to take any action.

Vivek

>  }
>  
>  static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
> -- 
> 2.27.0
>