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From:   "Benjamin Coddington" <bcodding@redhat.com>
To:     trondmy@kernel.org
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH 02/12] NFS: Clean up readdir struct nfs_cache_array
Date:   Tue, 03 Nov 2020 08:35:27 -0500
Message-ID: <015FB69A-1E45-4A93-89F3-2755F2A565F0@redhat.com>
In-Reply-To: <20201102180658.6218-3-trondmy@kernel.org>
References: <20201102180658.6218-1-trondmy@kernel.org>
 <20201102180658.6218-2-trondmy@kernel.org>
 <20201102180658.6218-3-trondmy@kernel.org>
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On 2 Nov 2020, at 13:06, trondmy@kernel.org wrote:

> From: Trond Myklebust <trond.myklebust@hammerspace.com>
>
> Since the 'eof_index' is only ever used as a flag, make it so.
> Also add a flag to detect if the page has been completely filled.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  fs/nfs/dir.c | 66 
> ++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 49 insertions(+), 17 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 67d8595cd6e5..604ebe015387 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -138,9 +138,10 @@ struct nfs_cache_array_entry {
>  };
>
>  struct nfs_cache_array {
> -	int size;
> -	int eof_index;
>  	u64 last_cookie;
> +	unsigned int size;
> +	unsigned char page_full : 1,
> +		      page_is_eof : 1;
>  	struct nfs_cache_array_entry array[];
>  };
>
> @@ -172,7 +173,6 @@ void nfs_readdir_init_array(struct page *page)
>
>  	array = kmap_atomic(page);
>  	memset(array, 0, sizeof(struct nfs_cache_array));
> -	array->eof_index = -1;
>  	kunmap_atomic(array);
>  }
>
> @@ -192,6 +192,17 @@ void nfs_readdir_clear_array(struct page *page)
>  	kunmap_atomic(array);
>  }
>
> +static void nfs_readdir_array_set_eof(struct nfs_cache_array *array)
> +{
> +	array->page_is_eof = 1;
> +	array->page_full = 1;
> +}
> +
> +static bool nfs_readdir_array_is_full(struct nfs_cache_array *array)
> +{
> +	return array->page_full;
> +}
> +
>  /*
>   * the caller is responsible for freeing qstr.name
>   * when called by nfs_readdir_add_to_array, the strings will be freed 
> in
> @@ -213,6 +224,23 @@ int nfs_readdir_make_qstr(struct qstr *string, 
> const char *name, unsigned int le
>  	return 0;
>  }
>
> +/*
> + * Check that the next array entry lies entirely within the page 
> bounds
> + */
> +static int nfs_readdir_array_can_expand(struct nfs_cache_array 
> *array)
> +{
> +	struct nfs_cache_array_entry *cache_entry;
> +
> +	if (array->page_full)
> +		return -ENOSPC;
> +	cache_entry = &array->array[array->size + 1];
> +	if ((char *)cache_entry - (char *)array > PAGE_SIZE) {
> +		array->page_full = 1;
> +		return -ENOSPC;
> +	}
> +	return 0;
> +}
> +

I think we could do this calculation at compile-time instead of doing it 
for
each entry, for dubious nominal gains..

Ben


>  static
>  int nfs_readdir_add_to_array(struct nfs_entry *entry, struct page 
> *page)
>  {
> @@ -220,13 +248,11 @@ int nfs_readdir_add_to_array(struct nfs_entry 
> *entry, struct page *page)
>  	struct nfs_cache_array_entry *cache_entry;
>  	int ret;
>
> -	cache_entry = &array->array[array->size];
> -
> -	/* Check that this entry lies within the page bounds */
> -	ret = -ENOSPC;
> -	if ((char *)&cache_entry[1] - (char *)page_address(page) > 
> PAGE_SIZE)
> +	ret = nfs_readdir_array_can_expand(array);
> +	if (ret)
>  		goto out;
>
> +	cache_entry = &array->array[array->size];
>  	cache_entry->cookie = entry->prev_cookie;
>  	cache_entry->ino = entry->ino;
>  	cache_entry->d_type = entry->d_type;
> @@ -236,12 +262,21 @@ int nfs_readdir_add_to_array(struct nfs_entry 
> *entry, struct page *page)
>  	array->last_cookie = entry->cookie;
>  	array->size++;
>  	if (entry->eof != 0)
> -		array->eof_index = array->size;
> +		nfs_readdir_array_set_eof(array);
>  out:
>  	kunmap(page);
>  	return ret;
>  }
>
> +static void nfs_readdir_page_set_eof(struct page *page)
> +{
> +	struct nfs_cache_array *array;
> +
> +	array = kmap_atomic(page);
> +	nfs_readdir_array_set_eof(array);
> +	kunmap_atomic(array);
> +}
> +
>  static inline
>  int is_32bit_api(void)
>  {
> @@ -270,7 +305,7 @@ int nfs_readdir_search_for_pos(struct 
> nfs_cache_array *array, nfs_readdir_descri
>  	if (diff < 0)
>  		goto out_eof;
>  	if (diff >= array->size) {
> -		if (array->eof_index >= 0)
> +		if (array->page_is_eof)
>  			goto out_eof;
>  		return -EAGAIN;
>  	}
> @@ -334,7 +369,7 @@ int nfs_readdir_search_for_cookie(struct 
> nfs_cache_array *array, nfs_readdir_des
>  			return 0;
>  		}
>  	}
> -	if (array->eof_index >= 0) {
> +	if (array->page_is_eof) {
>  		status = -EBADCOOKIE;
>  		if (desc->dir_cookie == array->last_cookie)
>  			desc->eof = true;
> @@ -566,7 +601,6 @@ int 
> nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct 
> nfs_entry *en
>  	struct xdr_stream stream;
>  	struct xdr_buf buf;
>  	struct page *scratch;
> -	struct nfs_cache_array *array;
>  	unsigned int count = 0;
>  	int status;
>
> @@ -604,10 +638,8 @@ int 
> nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct 
> nfs_entry *en
>
>  out_nopages:
>  	if (count == 0 || (status == -EBADCOOKIE && entry->eof != 0)) {
> -		array = kmap(page);
> -		array->eof_index = array->size;
> +		nfs_readdir_page_set_eof(page);
>  		status = 0;
> -		kunmap(page);
>  	}
>
>  	put_page(scratch);
> @@ -689,7 +721,7 @@ int 
> nfs_readdir_xdr_to_array(nfs_readdir_descriptor_t *desc, struct page 
> *page,
>  				status = 0;
>  			break;
>  		}
> -	} while (array->eof_index < 0);
> +	} while (!nfs_readdir_array_is_full(array));
>
>  	nfs_readdir_free_pages(pages, array_size);
>  out_release_array:
> @@ -825,7 +857,7 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc)
>  		if (desc->duped != 0)
>  			desc->duped = 1;
>  	}
> -	if (array->eof_index >= 0)
> +	if (array->page_is_eof)
>  		desc->eof = true;
>
>  	kunmap(desc->page);
> -- 
> 2.28.0