ext4: drop ec_type from the ext4_ext_cache structure

We can encode the ec_type information by using ee_len == 0 to denote
EXT4_EXT_CACHE_NO, ee_start == 0 to denote EXT4_EXT_CACHE_GAP, and if
neither is true, then the cache type must be EXT4_EXT_CACHE_EXTENT.
This allows us to reduce the size of ext4_ext_inode by another 8
bytes.  (ec_type is 4 bytes, plus another 4 bytes of padding)
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -738,12 +738,13 @@ do {									       \
 
 /*
  * storage for cached extent
+ * If ec_len == 0, then the cache is invalid.
+ * If ec_start == 0, then the cache represents a gap (null mapping)
  */
 struct ext4_ext_cache {
 	ext4_fsblk_t	ec_start;
 	ext4_lblk_t	ec_block;
 	__u32		ec_len; /* must be 32bit to return holes */
-	__u32		ec_type;
 };
 
 /*

fs/ext4/ext4_extents.h

@@ -119,10 +119,6 @@ struct ext4_ext_path {
  * structure for external API
  */
 
-#define EXT4_EXT_CACHE_NO	0
-#define EXT4_EXT_CACHE_GAP	1
-#define EXT4_EXT_CACHE_EXTENT	2
-
 /*
  * to be called by ext4_ext_walk_space()
  * negative retcode - error
@@ -197,7 +193,7 @@ static inline unsigned short ext_depth(struct inode *inode)
 static inline void
 ext4_ext_invalidate_cache(struct inode *inode)
 {
-	EXT4_I(inode)->i_cached_extent.ec_type = EXT4_EXT_CACHE_NO;
+	EXT4_I(inode)->i_cached_extent.ec_len = 0;
 }
 
 static inline void ext4_ext_mark_uninitialized(struct ext4_extent *ext)

fs/ext4/extents.c

@@ -1894,12 +1894,10 @@ static int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t block,
 			cbex.ec_block = start;
 			cbex.ec_len = end - start;
 			cbex.ec_start = 0;
-			cbex.ec_type = EXT4_EXT_CACHE_GAP;
 		} else {
 			cbex.ec_block = le32_to_cpu(ex->ee_block);
 			cbex.ec_len = ext4_ext_get_actual_len(ex);
 			cbex.ec_start = ext4_ext_pblock(ex);
-			cbex.ec_type = EXT4_EXT_CACHE_EXTENT;
 		}
 
 		if (unlikely(cbex.ec_len == 0)) {
@@ -1939,13 +1937,12 @@ static int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t block,
 
 static void
 ext4_ext_put_in_cache(struct inode *inode, ext4_lblk_t block,
-			__u32 len, ext4_fsblk_t start, int type)
+			__u32 len, ext4_fsblk_t start)
 {
 	struct ext4_ext_cache *cex;
 	BUG_ON(len == 0);
 	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 	cex = &EXT4_I(inode)->i_cached_extent;
-	cex->ec_type = type;
 	cex->ec_block = block;
 	cex->ec_len = len;
 	cex->ec_start = start;
@@ -1998,15 +1995,18 @@ ext4_ext_put_gap_in_cache(struct inode *inode, struct ext4_ext_path *path,
 	}
 
 	ext_debug(" -> %u:%lu\n", lblock, len);
-	ext4_ext_put_in_cache(inode, lblock, len, 0, EXT4_EXT_CACHE_GAP);
+	ext4_ext_put_in_cache(inode, lblock, len, 0);
 }
 
+/*
+ * Return 0 if cache is invalid; 1 if the cache is valid
+ */
 static int
 ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
 			struct ext4_extent *ex)
 {
 	struct ext4_ext_cache *cex;
-	int ret = EXT4_EXT_CACHE_NO;
+	int ret = 0;
 
 	/*
 	 * We borrow i_block_reservation_lock to protect i_cached_extent
@@ -2015,11 +2015,9 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
 	cex = &EXT4_I(inode)->i_cached_extent;
 
 	/* has cache valid data? */
-	if (cex->ec_type == EXT4_EXT_CACHE_NO)
+	if (cex->ec_len == 0)
 		goto errout;
 
-	BUG_ON(cex->ec_type != EXT4_EXT_CACHE_GAP &&
-			cex->ec_type != EXT4_EXT_CACHE_EXTENT);
 	if (in_range(block, cex->ec_block, cex->ec_len)) {
 		ex->ee_block = cpu_to_le32(cex->ec_block);
 		ext4_ext_store_pblock(ex, cex->ec_start);
@@ -2027,7 +2025,7 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
 		ext_debug("%u cached by %u:%u:%llu\n",
 				block,
 				cex->ec_block, cex->ec_len, cex->ec_start);
-		ret = cex->ec_type;
+		ret = 1;
 	}
 errout:
 	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
@@ -3298,7 +3296,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	struct ext4_extent_header *eh;
 	struct ext4_extent newex, *ex;
 	ext4_fsblk_t newblock;
-	int err = 0, depth, ret, cache_type;
+	int err = 0, depth, ret;
 	unsigned int allocated = 0;
 	struct ext4_allocation_request ar;
 	ext4_io_end_t *io = EXT4_I(inode)->cur_aio_dio;
@@ -3307,9 +3305,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 		  map->m_lblk, map->m_len, inode->i_ino);
 
 	/* check in cache */
-	cache_type = ext4_ext_in_cache(inode, map->m_lblk, &newex);
-	if (cache_type) {
-		if (cache_type == EXT4_EXT_CACHE_GAP) {
+	if (ext4_ext_in_cache(inode, map->m_lblk, &newex)) {
+		if (!newex.ee_start_lo && !newex.ee_start_hi) {
 			if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
 				/*
 				 * block isn't allocated yet and
@@ -3318,7 +3315,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 				goto out2;
 			}
 			/* we should allocate requested block */
-		} else if (cache_type == EXT4_EXT_CACHE_EXTENT) {
+		} else {
 			/* block is already allocated */
 			newblock = map->m_lblk
 				   - le32_to_cpu(newex.ee_block)
@@ -3327,8 +3324,6 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 			allocated = ext4_ext_get_actual_len(&newex) -
 				(map->m_lblk - le32_to_cpu(newex.ee_block));
 			goto out;
-		} else {
-			BUG();
 		}
 	}
 
@@ -3379,8 +3374,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 			/* Do not put uninitialized extent in the cache */
 			if (!ext4_ext_is_uninitialized(ex)) {
 				ext4_ext_put_in_cache(inode, ee_block,
-							ee_len, ee_start,
-							EXT4_EXT_CACHE_EXTENT);
+							ee_len, ee_start);
 				goto out;
 			}
 			ret = ext4_ext_handle_uninitialized_extents(handle,
@@ -3512,8 +3506,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	 * when it is _not_ an uninitialized extent.
 	 */
 	if ((flags & EXT4_GET_BLOCKS_UNINIT_EXT) == 0) {
-		ext4_ext_put_in_cache(inode, map->m_lblk, allocated, newblock,
-						EXT4_EXT_CACHE_EXTENT);
+		ext4_ext_put_in_cache(inode, map->m_lblk, allocated, newblock);
 		ext4_update_inode_fsync_trans(handle, inode, 1);
 	} else
 		ext4_update_inode_fsync_trans(handle, inode, 0);
@@ -3789,7 +3782,7 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
 
 	logical =  (__u64)newex->ec_block << blksize_bits;
 
-	if (newex->ec_type == EXT4_EXT_CACHE_GAP) {
+	if (newex->ec_start == 0) {
 		pgoff_t offset;
 		struct page *page;
 		struct buffer_head *bh = NULL;