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>

3 files changed, 18 insertions, 28 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 746a59853a07..de937fc10503 100644
--- a/fs/ext4/ext4.h
+++ b/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;
 };
 
 /*
diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index dfdda1766927..2e29abb30f76 100644
--- a/fs/ext4/ext4_extents.h
+++ b/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)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index f1a4354ea3cf..9081d1060a5f 100644
--- a/fs/ext4/extents.c
+++ b/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;