linux-kernel - Re: [PATCH v5 2/2] fuse: add new function to invalidate cache for all inodes

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Message-ID: <3fac8c84-2c41-461d-92f1-255903fc62a9@ddn.com>
Date: Mon, 17 Feb 2025 01:40:06 +0100
From: Bernd Schubert <bschubert@....com>
To: Luis Henriques <luis@...lia.com>, Miklos Szeredi <miklos@...redi.hu>
Cc: Dave Chinner <david@...morbit.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Matt Harvey <mharvey@...ptrading.com>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/2] fuse: add new function to invalidate cache for all
 inodes



On 2/16/25 17:50, 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 sb dcache.
> 
> Signed-off-by: Luis Henriques <luis@...lia.com>
> ---
>  fs/fuse/inode.c           | 33 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/fuse.h |  3 +++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index e9db2cb8c150..01a4dc5677ae 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -547,6 +547,36 @@ 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 inode *inode;
> +
> +	inode = fuse_ilookup(fc, FUSE_ROOT_ID, &fm);
> +	if (!inode || !fm)
> +		return -ENOENT;
> +
> +	/* Remove all possible active references to cached inodes */
> +	shrink_dcache_sb(fm->sb);
> +
> +	/* Remove all unreferenced inodes from cache */
> +	invalidate_inodes(fm->sb);
> +
> +	return 0;
> +}
> +
> +/*
> + * Notify to invalidate inodes cache.  It can be called with @nodeid set to
> + * either:
> + *
> + * - An inode number - Any pending writebacks within the rage [@offset @len]
> + *   will be triggered and the inode will be validated.  To invalidate the whole
> + *   cache @offset has to be set to '0' and @len needs to be <= '0'; if @offset
> + *   is negative, only the inode attributes are invalidated.
> + *
> + * - FUSE_INVAL_ALL_INODES - All the inodes in the superblock are invalidated
> + *   and the whole dcache is shrinked.
> + */
>  int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
>  			     loff_t offset, loff_t len)
>  {
> @@ -555,6 +585,9 @@ 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 5e0eb41d967e..e5852b63f99f 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -669,6 +669,9 @@ 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
>  


I think this version might end up in 

static void fuse_evict_inode(struct inode *inode)
{
	struct fuse_inode *fi = get_fuse_inode(inode);

	/* Will write inode on close/munmap and in all other dirtiers */
	WARN_ON(inode->i_state & I_DIRTY_INODE);


if the fuse connection has writeback cache enabled.


Without having it tested, reproducer would probably be to run
something like passthrough_hp (without --direct-io), opening
and writing to a file and then sending FUSE_INVAL_ALL_INODES.



Thanks,
Bernd