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>

5 files changed, 43 insertions, 16 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 2fb531cfd48b..32b7daa41a42 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -811,7 +811,7 @@ struct ext4_inode_info {
          */
         struct rw_semaphore i_data_sem;
         struct inode vfs_inode;
-        struct jbd2_inode jinode;
+        struct jbd2_inode *jinode;
 
         struct ext4_ext_cache i_cached_extent;
         /*
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index b0bd792c58c5..d8b992e658c1 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -253,7 +253,7 @@ static inline int ext4_journal_force_commit(journal_t *journal)
 static inline int ext4_jbd2_file_inode(handle_t *handle, struct inode *inode)
 {
         if (ext4_handle_valid(handle))
-                return jbd2_journal_file_inode(handle, &EXT4_I(inode)->jinode);
+                return jbd2_journal_file_inode(handle, EXT4_I(inode)->jinode);
         return 0;
 }
 
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 5a5c55ddceef..bb003dc9ffff 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -104,6 +104,7 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 {
         struct super_block *sb = inode->i_sb;
         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+        struct ext4_inode_info *ei = EXT4_I(inode);
         struct vfsmount *mnt = filp->f_path.mnt;
         struct path path;
         char buf[64], *cp;
@@ -127,6 +128,27 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
                         ext4_mark_super_dirty(sb);
                 }
         }
+        /*
+         * Set up the jbd2_inode if we are opening the inode for
+         * writing and the journal is present
+         */
+        if (sbi->s_journal && !ei->jinode && (filp->f_mode & FMODE_WRITE)) {
+                struct jbd2_inode *jinode = jbd2_alloc_inode(GFP_KERNEL);
+
+                spin_lock(&inode->i_lock);
+                if (!ei->jinode) {
+                        if (!jinode) {
+                                spin_unlock(&inode->i_lock);
+                                return -ENOMEM;
+                        }
+                        ei->jinode = jinode;
+                        jbd2_journal_init_jbd_inode(ei->jinode, inode);
+                        jinode = NULL;
+                }
+                spin_unlock(&inode->i_lock);
+                if (unlikely(jinode != NULL))
+                        jbd2_free_inode(jinode);
+        }
         return dquot_file_open(inode, filp);
 }
 
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);
         }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f5960d673e4e..1cd4326c530b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -818,12 +818,6 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
         memset(&ei->i_cached_extent, 0, sizeof(struct ext4_ext_cache));
         INIT_LIST_HEAD(&ei->i_prealloc_list);
         spin_lock_init(&ei->i_prealloc_lock);
-        /*
-         * Note:  We can be called before EXT4_SB(sb)->s_journal is set,
-         * therefore it can be null here.  Don't check it, just initialize
-         * jinode.
-         */
-        jbd2_journal_init_jbd_inode(&ei->jinode, &ei->vfs_inode);
         ei->i_reserved_data_blocks = 0;
         ei->i_reserved_meta_blocks = 0;
         ei->i_allocated_meta_blocks = 0;
@@ -832,6 +826,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
 #ifdef CONFIG_QUOTA
         ei->i_reserved_quota = 0;
 #endif
+        ei->jinode = NULL;
         INIT_LIST_HEAD(&ei->i_completed_io_list);
         spin_lock_init(&ei->i_completed_io_lock);
         ei->cur_aio_dio = NULL;
@@ -900,9 +895,12 @@ void ext4_clear_inode(struct inode *inode)
         end_writeback(inode);
         dquot_drop(inode);
         ext4_discard_preallocations(inode);
-        if (EXT4_JOURNAL(inode))
-                jbd2_journal_release_jbd_inode(EXT4_SB(inode->i_sb)->s_journal,
-                                       &EXT4_I(inode)->jinode);
+        if (EXT4_I(inode)->jinode) {
+                jbd2_journal_release_jbd_inode(EXT4_JOURNAL(inode),
+                                               EXT4_I(inode)->jinode);
+                jbd2_free_inode(EXT4_I(inode)->jinode);
+                EXT4_I(inode)->jinode = NULL;
+        }
 }
 
 static inline void ext4_show_quota_options(struct seq_file *seq,