Re: [PATCH 11/11] NFS: Bring back nfs_dir_mapping_need_revalidate() in nfs_readdir()

["Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>]

Hi Dave,

----- Original Message -----
> From: "David Wysochanski" <dwysocha@redhat.com>
> To: "trondmy" <trondmy@hammerspace.com>, "Anna Schumaker" <anna.schumaker@netapp.com>
> Cc: "linux-nfs" <linux-nfs@vger.kernel.org>
> Sent: Monday, 2 November, 2020 14:50:11
> Subject: [PATCH 11/11] NFS: Bring back nfs_dir_mapping_need_revalidate() in nfs_readdir()

> commit 79f687a3de9e ("NFS: Fix a performance regression in readdir")
> removed nfs_dir_mapping_need_revalidate() in an attempt to fix a
> performance regression, but had the effect that with NFSv3 the
> pagecache would never expire while a process was reading a directory.
> An earlier patch addressed this problem by allowing the pagecache
> to expire but the current process to continue using the last cookie
> returned by the server when searching the pagecache, rather than
> always starting at 0.  Thus, bring back nfs_dir_mapping_need_revalidate()
> so that nfsi->cache_validity & NFS_INO_INVALID_DATA will be seen
> and nfs_revalidate_mapping() will be called with NFSv3 as well,
> making it behave the same as NFSv4.
> 
> Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
> ---
> fs/nfs/dir.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index cbd74cbdbb9f..aeb086fb3d0a 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -872,6 +872,17 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc)
> 	return status;
> }
> 
> +static bool nfs_dir_mapping_need_revalidate(struct inode *dir)
> +{
> +	struct nfs_inode *nfsi = NFS_I(dir);
> +
> +	if (nfs_attribute_cache_expired(dir))
> +		return true;
> +	if (nfsi->cache_validity & NFS_INO_INVALID_DATA)
> +		return true;
> +	return false;
> +}

Is this the same as:

static bool nfs_dir_mapping_need_revalidate(struct inode *dir)
{
        struct nfs_inode *nfsi = NFS_I(dir);

        return nfs_attribute_cache_expired(dir) || nfsi->cache_validity & NFS_INO_INVALID_DATA);
}

Tigran.

> +
> /* The file offset position represents the dirent entry number.  A
>    last cookie cache takes care of the common case of reading the
>    whole directory.
> @@ -903,7 +914,7 @@ static int nfs_readdir(struct file *file, struct dir_context
> *ctx)
> 	 * to either find the entry with the appropriate number or
> 	 * revalidate the cookie.
> 	 */
> -	if (ctx->pos == 0 || nfs_attribute_cache_expired(inode))
> +	if (ctx->pos == 0 || nfs_dir_mapping_need_revalidate(inode))
> 		res = nfs_revalidate_mapping(inode, file->f_mapping);
> 	if (res < 0)
> 		goto out;
> --
> 1.8.3.1