ext4: drop i_state_flags on architectures with 64-bit longs

We can store the dynamic inode state flags in the high bits of
EXT4_I(inode)->i_flags, and eliminate i_state_flags.  This saves 8
bytes from the size of ext4_inode_info structure, which when
multiplied by the number of the number of in the inode cache, can save
a lot of memory.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -764,7 +764,9 @@ struct ext4_inode_info {
 	 */
 	ext4_group_t	i_block_group;
 	ext4_lblk_t	i_dir_start_lookup;
+#if (BITS_PER_LONG < 64)
 	unsigned long	i_state_flags;		/* Dynamic state flags */
+#endif
 	unsigned long	i_flags;
 
 #ifdef CONFIG_EXT4_FS_XATTR
@@ -1239,22 +1241,36 @@ enum {
 	EXT4_STATE_DELALLOC_RESERVED,	/* blks already reserved for delalloc */
 };
 
-#define EXT4_INODE_BIT_FNS(name, field)					\
+#define EXT4_INODE_BIT_FNS(name, field, offset)				\
 static inline int ext4_test_inode_##name(struct inode *inode, int bit)	\
 {									\
-	return test_bit(bit, &EXT4_I(inode)->i_##field);		\
+	return test_bit(bit + (offset), &EXT4_I(inode)->i_##field);	\
 }									\
 static inline void ext4_set_inode_##name(struct inode *inode, int bit)	\
 {									\
-	set_bit(bit, &EXT4_I(inode)->i_##field);			\
+	set_bit(bit + (offset), &EXT4_I(inode)->i_##field);		\
 }									\
 static inline void ext4_clear_inode_##name(struct inode *inode, int bit) \
 {									\
-	clear_bit(bit, &EXT4_I(inode)->i_##field);			\
+	clear_bit(bit + (offset), &EXT4_I(inode)->i_##field);		\
 }
 
-EXT4_INODE_BIT_FNS(flag, flags)
-EXT4_INODE_BIT_FNS(state, state_flags)
+EXT4_INODE_BIT_FNS(flag, flags, 0)
+#if (BITS_PER_LONG < 64)
+EXT4_INODE_BIT_FNS(state, state_flags, 0)
+
+static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
+{
+	(ei)->i_state_flags = 0;
+}
+#else
+EXT4_INODE_BIT_FNS(state, flags, 32)
+
+static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
+{
+	/* We depend on the fact that callers will set i_flags */
+}
+#endif
 #else
 /* Assume that user mode programs are passing in an ext4fs superblock, not
  * a kernel struct super_block.  This will allow us to call the feature-test

fs/ext4/ialloc.c

@@ -1027,7 +1027,7 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode,
 	inode->i_generation = sbi->s_next_generation++;
 	spin_unlock(&sbi->s_next_gen_lock);
 
-	ei->i_state_flags = 0;
+	ext4_clear_state_flags(ei); /* Only relevant on 32-bit archs */
 	ext4_set_inode_state(inode, EXT4_STATE_NEW);
 
 	ei->i_extra_isize = EXT4_SB(sb)->s_want_extra_isize;

fs/ext4/inode.c

@@ -4868,7 +4868,7 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 	}
 	inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
 
-	ei->i_state_flags = 0;
+	ext4_clear_state_flags(ei);	/* Only relevant on 32-bit archs */
 	ei->i_dir_start_lookup = 0;
 	ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
 	/* We now have enough fields to check if the inode was active or not.
@@ -5127,7 +5127,7 @@ static int ext4_do_update_inode(handle_t *handle,
 	if (ext4_inode_blocks_set(handle, raw_inode, ei))
 		goto out_brelse;
 	raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
-	raw_inode->i_flags = cpu_to_le32(ei->i_flags);
+	raw_inode->i_flags = cpu_to_le32(ei->i_flags & 0xFFFFFFFF);
 	if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
 	    cpu_to_le32(EXT4_OS_HURD))
 		raw_inode->i_file_acl_high =