Re: [PATCH v3 04/10] fscrypt: Drop d_revalidate once the key is added

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Jan 19, 2024 at 03:47:36PM -0300, Gabriel Krisman Bertazi wrote:
> /*
>  * When d_splice_alias() moves a directory's no-key alias to its plaintext alias
>  * as a result of the encryption key being added, DCACHE_NOKEY_NAME must be
>  * cleared.  Note that we don't have to support arbitrary moves of this flag
>  * because fscrypt doesn't allow no-key names to be the source or target of a
>  * rename().
>  */
>  static inline void fscrypt_handle_d_move(struct dentry *dentry)
>  {
>  	dentry->d_flags &= ~DCACHE_NOKEY_NAME;
> +
> +	/*
> +	 * Save the d_revalidate call cost during VFS operations.  We
> +	 * can do it because, when the key is available, the dentry
> +	 * can't go stale and the key won't go away without eviction.
> +	 */
> +	if (dentry->d_op && dentry->d_op->d_revalidate == fscrypt_d_revalidate)
> +		dentry->d_flags &= ~DCACHE_OP_REVALIDATE;
>  }

Is there any way to optimize this further for the case where fscrypt is not
being used?  This is called unconditionally from d_move().  I've generally been
trying to avoid things like this where the fscrypt support slows things down for
everyone even when they're not using the feature.

In any case, as always please don't let function comments get outdated.  Since
it now seems to just describe the DCACHE_NOKEY_NAME clearing and not the whole
function, maybe it should be moved to above that line.

- Eric