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>

3 files changed, 25 insertions, 9 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 50e3d24483fb..2fb531cfd48b 100644
--- a/fs/ext4/ext4.h
+++ b/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
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 1ce240a23ebb..eb9097aec6f0 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -1027,7 +1027,7 @@ got:
         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;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3ae83137cf34..0801ee6a173e 100644
--- a/fs/ext4/inode.c
+++ b/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 =