ext4: dynamically allocate the jbd2_inode in ext4_inode_info as necessary

Replace the jbd2_inode structure (which is 48 bytes) with a pointer
and only allocate the jbd2_inode when it is needed --- that is, when
the file system has a journal present and the inode has been opened
for writing.  This allows us to further slim down the ext4_inode_info
structure.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 12 insertions, 5 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0801ee6a173e..2693fcda30d8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -55,10 +55,17 @@ static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                               loff_t new_size)
 {
         trace_ext4_begin_ordered_truncate(inode, new_size);
-        return jbd2_journal_begin_ordered_truncate(
-                                        EXT4_SB(inode->i_sb)->s_journal,
-                                        &EXT4_I(inode)->jinode,
-                                        new_size);
+        /*
+         * If jinode is zero, then we never opened the file for
+         * writing, so there's no need to call
+         * jbd2_journal_begin_ordered_truncate() since there's no
+         * outstanding writes we need to flush.
+         */
+        if (!EXT4_I(inode)->jinode)
+                return 0;
+        return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
+                                                   EXT4_I(inode)->jinode,
+                                                   new_size);
 }
 
 static void ext4_invalidatepage(struct page *page, unsigned long offset);
@@ -4054,7 +4061,7 @@ int ext4_block_truncate_page(handle_t *handle,
         if (ext4_should_journal_data(inode)) {
                 err = ext4_handle_dirty_metadata(handle, inode, bh);
         } else {
-                if (ext4_should_order_data(inode))
+                if (ext4_should_order_data(inode) && EXT4_I(inode)->jinode)
                         err = ext4_jbd2_file_inode(handle, inode);
                 mark_buffer_dirty(bh);
         }