f2fs: don't reserve additional space in xattr block

In this patch, we change xattr block disk layout as below:

Before:
			xattr node block layout
+---------------------------------------------+---------------+-------------+
|           node block xattr entries          |   reserved    | node footer |
|                  4068 Bytes                 |    4 Bytes    |  24 Bytes   |

			In memory layout
+--------------------+---------------------------------+--------------------+
|    inline xattr    |     node block xattr entries    |      reserved      |
|     200 Bytes      |         4068 Bytes              |      4 Bytes       |

After:
			xattr node block layout
+-------------------------------------------------------------+-------------+
|                  node block xattr entries                   | node footer |
|                         4072 Bytes                          |  24 Bytes   |

			In memory layout
+--------------------+---------------------------------+--------------------+
|    inline xattr    |     node block xattr entries    |      reserved      |
|     200 Bytes      |         4072 Bytes              |      4 Bytes       |

With this change, we don't need to reserve additional space in node block,
just keep reserved space in logical in-memory layout. So that it would help
to enlarge valid free space of xattr node block.

As tested, generic/026 shows max stored xattr entires number increases from
531 to 532 when inline_xattr option is enabled.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/xattr.c

@@ -256,7 +256,7 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
 	if (!size && !inline_size)
 		return -ENODATA;
 
-	txattr_addr = kzalloc(inline_size + size + RESERVED_XATTR_SIZE,
+	txattr_addr = kzalloc(inline_size + size + XATTR_PADDING_SIZE,
 							GFP_F2FS_ZERO);
 	if (!txattr_addr)
 		return -ENOMEM;
@@ -332,7 +332,7 @@ static int read_all_xattrs(struct inode *inode, struct page *ipage,
 	void *txattr_addr;
 	int err;
 
-	txattr_addr = kzalloc(inline_size + size + RESERVED_XATTR_SIZE,
+	txattr_addr = kzalloc(inline_size + size + XATTR_PADDING_SIZE,
 							GFP_F2FS_ZERO);
 	if (!txattr_addr)
 		return -ENOMEM;
@@ -451,7 +451,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
 	}
 
 	xattr_addr = page_address(xpage);
-	memcpy(xattr_addr, txattr_addr + inline_size, MAX_XATTR_BLOCK_SIZE);
+	memcpy(xattr_addr, txattr_addr + inline_size, VALID_XATTR_BLOCK_SIZE);
 	set_page_dirty(xpage);
 	f2fs_put_page(xpage, 1);
 

fs/f2fs/xattr.h

@@ -72,9 +72,8 @@ struct f2fs_xattr_entry {
 		for (entry = XATTR_FIRST_ENTRY(addr);\
 				!IS_XATTR_LAST_ENTRY(entry);\
 				entry = XATTR_NEXT_ENTRY(entry))
-#define MAX_XATTR_BLOCK_SIZE	(PAGE_SIZE - sizeof(struct node_footer))
-#define RESERVED_XATTR_SIZE	(sizeof(__u32))
-#define VALID_XATTR_BLOCK_SIZE	(MAX_XATTR_BLOCK_SIZE - RESERVED_XATTR_SIZE)
+#define VALID_XATTR_BLOCK_SIZE	(PAGE_SIZE - sizeof(struct node_footer))
+#define XATTR_PADDING_SIZE	(sizeof(__u32))
 #define MIN_OFFSET(i)		XATTR_ALIGN(inline_xattr_size(i) +	\
 						VALID_XATTR_BLOCK_SIZE)