jbd2: add support for avoiding data writes during transaction commits

Currently when filesystem needs to make sure data is on permanent
storage before committing a transaction it adds inode to transaction's
inode list. During transaction commit, jbd2 writes back all dirty
buffers that have allocated underlying blocks and waits for the IO to
finish. However when doing writeback for delayed allocated data, we
allocate blocks and immediately submit the data. Thus asking jbd2 to
write dirty pages just unnecessarily adds more work to jbd2 possibly
writing back other redirtied blocks.

Add support to jbd2 to allow filesystem to ask jbd2 to only wait for
outstanding data writes before committing a transaction and thus avoid
unnecessary writes.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 2ad98d6e19f4..70078096117d 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -219,6 +219,8 @@ static int journal_submit_data_buffers(journal_t *journal,
 
         spin_lock(&journal->j_list_lock);
         list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
+                if (!(jinode->i_flags & JI_WRITE_DATA))
+                        continue;
                 mapping = jinode->i_vfs_inode->i_mapping;
                 jinode->i_flags |= JI_COMMIT_RUNNING;
                 spin_unlock(&journal->j_list_lock);
@@ -256,6 +258,8 @@ static int journal_finish_inode_data_buffers(journal_t *journal,
         /* For locking, see the comment in journal_submit_data_buffers() */
         spin_lock(&journal->j_list_lock);
         list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
+                if (!(jinode->i_flags & JI_WAIT_DATA))
+                        continue;
                 jinode->i_flags |= JI_COMMIT_RUNNING;
                 spin_unlock(&journal->j_list_lock);
                 err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);