linux-kernel - Re: [RFC PATCH v2] fuse: add optional workqueue to periodically invalidate expired dentries

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Message-ID: <CAJfpeguD6jR7AQ=BWs-nKyT4ZV4d35KLM9UPZNzMd-SkcngmzQ@mail.gmail.com>
Date: Tue, 13 May 2025 11:56:02 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Luis Henriques <luis@...lia.com>
Cc: Bernd Schubert <bernd@...ernd.com>, Laura Promberger <laura.promberger@...n.ch>, 
	Dave Chinner <david@...morbit.com>, Matt Harvey <mharvey@...ptrading.com>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kernel-dev@...lia.com
Subject: Re: [RFC PATCH v2] fuse: add optional workqueue to periodically
 invalidate expired dentries

On Tue, 15 Apr 2025 at 15:38, Luis Henriques <luis@...lia.com> wrote:

> +inval_wq=N
> +  Enable a workqueue that will periodically invalidate dentries that
> +  have expired.  'N' is a value in seconds and has to be bigger than
> +  5 seconds.
> +

I don't think a mount option is needed.  Perhaps a module option knob
instead is sufficient?

> +static void fuse_dentry_tree_add_node(struct dentry *dentry)
> +{
> +       struct fuse_conn *fc = get_fuse_conn_super(dentry->d_sb);
> +       struct dentry_node *dn, *cur;
> +       struct rb_node **p, *parent = NULL;
> +       bool start_work = false;
> +
> +       if (!fc->inval_wq)
> +               return;
> +
> +       dn = kmalloc(sizeof(*dn), GFP_KERNEL);
> +       if (!dn)
> +               return;
> +       dn->dentry = dget(dentry);

A dentry ref without a vfsmount ref is generally bad idea.

Instead of acquiring a ref, the lifetime of dn should be tied to that
of the dentry (hook into ->d_prune).

So just put the rb_node in fuse_dentry and get rid of the "#if
BITS_PER_LONG >= 64" optimization.

Thanks,
Miklos