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

[Luis Henriques <luis@igalia.com>]

Hi Miklos,

On Wed, Jan 15 2025, 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.

Gentle ping, any comments on how to improve/modify this patch so that it
could eventually be acceptable in mainline?

Cheers,
-- 
Luís

>
> Signed-off-by: Luis Henriques <luis@igalia.com>
> ---
> 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@fromorbit.com
>
>  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) {
> +		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);
> +
> +	shrink_dcache_sb(sb);
> +
> +	return 0;
> +}
> +
>  int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
>  			     loff_t offset, loff_t len)
>  {
> @@ -554,6 +604,9 @@ int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
>  	pgoff_t pg_start;
>  	pgoff_t pg_end;
>  
> +	if (nodeid == FUSE_INVAL_ALL_INODES)
> +		return fuse_reverse_inval_all(fc);
> +
>  	inode = fuse_ilookup(fc, nodeid, NULL);
>  	if (!inode)
>  		return -ENOENT;
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index f1e99458e29e..e9e78292d107 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -658,6 +658,9 @@ enum fuse_notify_code {
>  	FUSE_NOTIFY_CODE_MAX,
>  };
>  
> +/* The nodeid to request to invalidate all inodes */
> +#define FUSE_INVAL_ALL_INODES 0
> +
>  /* The read buffer is required to be at least 8k, but may be much larger */
>  #define FUSE_MIN_READ_BUFFER 8192
>