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From:   "Benjamin Coddington" <bcodding@redhat.com>
To:     trondmy@kernel.org
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH v2 05/16] NFS: Don't discard readdir results
Date:   Tue, 03 Nov 2020 10:55:21 -0500
Message-ID: <DEB8710B-8D01-4FC9-9DA6-78A701C46E19@redhat.com>
In-Reply-To: <20201103153329.531942-6-trondmy@kernel.org>
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 <20201103153329.531942-2-trondmy@kernel.org>
 <20201103153329.531942-3-trondmy@kernel.org>
 <20201103153329.531942-4-trondmy@kernel.org>
 <20201103153329.531942-5-trondmy@kernel.org>
 <20201103153329.531942-6-trondmy@kernel.org>
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On 3 Nov 2020, at 10:33, trondmy@kernel.org wrote:

> From: Trond Myklebust <trond.myklebust@hammerspace.com>
>
> If a readdir call returns more data than we can fit into one page
> cache page, then allocate a new one for that data rather than
> discarding the data.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  fs/nfs/dir.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index b4861a33ad60..788c2a2eeaa3 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -321,6 +321,26 @@ static void nfs_readdir_page_set_eof(struct page 
> *page)
>  	kunmap_atomic(array);
>  }
>
> +static void nfs_readdir_page_unlock_and_put(struct page *page)
> +{
> +	unlock_page(page);
> +	put_page(page);
> +}
> +
> +static struct page *nfs_readdir_page_get_next(struct address_space 
> *mapping,
> +					      pgoff_t index, u64 cookie)
> +{
> +	struct page *page;
> +
> +	page = nfs_readdir_page_get_locked(mapping, index, cookie);
> +	if (page) {
> +		if (nfs_readdir_page_last_cookie(page) == cookie)
> +			return page;
> +		nfs_readdir_page_unlock_and_put(page);
> +	}
> +	return NULL;
> +}
> +
>  static inline
>  int is_32bit_api(void)
>  {
> @@ -638,13 +658,15 @@ void nfs_prime_dcache(struct dentry *parent, 
> struct nfs_entry *entry,
>  }
>
>  /* Perform conversion from xdr to cache array */
> -static
> -int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct 
> nfs_entry *entry,
> -				struct page **xdr_pages, struct page *page, unsigned int buflen)
> +static int nfs_readdir_page_filler(struct nfs_readdir_descriptor 
> *desc,
> +				   struct nfs_entry *entry,
> +				   struct page **xdr_pages,
> +				   struct page *fillme, unsigned int buflen)
>  {
> +	struct address_space *mapping = desc->file->f_mapping;
>  	struct xdr_stream stream;
>  	struct xdr_buf buf;
> -	struct page *scratch;
> +	struct page *scratch, *new, *page = fillme;
>  	int status;
>
>  	scratch = alloc_page(GFP_KERNEL);
> @@ -667,6 +689,19 @@ int 
> nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct 
> nfs_entry *en
>  					desc->dir_verifier);
>
>  		status = nfs_readdir_add_to_array(entry, page);
> +		if (status != -ENOSPC)
> +			continue;
> +
> +		if (page->mapping != mapping)
> +			break;

^^ How can this happen?

Ben