Re: [RFC PATCH] fuse: add new function to invalidate cache for all inodes

[Bernd Schubert]

On 1/15/25 17:32, Luis Henriques wrote:
> Currently userspace is able to notify the kernel to invalidate the cache
> for an inode.  This means that, if all the inodes in a filesystem need to
> be invalidated, then userspace needs to iterate through all of them and do
> this kernel notification separately.
> 
> This patch adds a new option that allows userspace to invalidate all the
> inodes with a single notification operation.  In addition to invalidate all
> the inodes, it also shrinks the superblock dcache.

Out of interest, what is the use case?

> 
> Signed-off-by: Luis Henriques <luis@xxxxxxxxxx>
> ---
> Just an additional note that this patch could eventually be simplified if
> Dave Chinner patch to iterate through the superblock inodes[1] is merged.
> 
> [1] https://lore.kernel.org/r/20241002014017.3801899-3-david@xxxxxxxxxxxxx
> 
>  fs/fuse/inode.c           | 53 +++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/fuse.h |  3 +++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 3ce4f4e81d09..1fd9a5f303da 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -546,6 +546,56 @@ struct inode *fuse_ilookup(struct fuse_conn *fc, u64 nodeid,
>  	return NULL;
>  }
>  
> +static int fuse_reverse_inval_all(struct fuse_conn *fc)
> +{
> +	struct fuse_mount *fm;
> +	struct super_block *sb;
> +	struct inode *inode, *old_inode = NULL;
> +	struct fuse_inode *fi;
> +
> +	inode = fuse_ilookup(fc, FUSE_ROOT_ID, NULL);
> +	if (!inode)
> +		return -ENOENT;
> +
> +	fm = get_fuse_mount(inode);
> +	iput(inode);
> +	if (!fm)
> +		return -ENOENT;
> +	sb = fm->sb;
> +
> +	spin_lock(&sb->s_inode_list_lock);
> +	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {

Maybe list_for_each_entry_safe() and then you can iput(inode) before the
next iteration?

> +		spin_lock(&inode->i_lock);
> +		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
> +		    !atomic_read(&inode->i_count)) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +
> +		__iget(inode);
> +		spin_unlock(&inode->i_lock);
> +		spin_unlock(&sb->s_inode_list_lock);
> +		iput(old_inode);
> +
> +		fi = get_fuse_inode(inode);
> +		spin_lock(&fi->lock);
> +		fi->attr_version = atomic64_inc_return(&fm->fc->attr_version);
> +		spin_unlock(&fi->lock);
> +		fuse_invalidate_attr(inode);
> +		forget_all_cached_acls(inode);
> +
> +		old_inode = inode;
> +		cond_resched();
> +		spin_lock(&sb->s_inode_list_lock);
> +	}
> +	spin_unlock(&sb->s_inode_list_lock);
> +	iput(old_inode);


Thanks,
Bernd