ext4: Allow ext4 to run without a journal

A few weeks ago I posted a patch for discussion that allowed ext4 to run
without a journal.  Since that time I've integrated the excellent
comments from Andreas and fixed several serious bugs.  We're currently
running with this patch and generating some performance numbers against
both ext2 (with backported reservations code) and ext4 with and without
a journal.  It just so happens that running without a journal is
slightly faster for most everything.

We did
	iozone -T -t 4 s 2g -r 256k -T -I -i0 -i1 -i2

which creates 4 threads, each of which create and do reads and writes on
a 2G file, with a buffer size of 256K, using O_DIRECT for all file opens
to bypass the page cache.  Results:

                     ext2        ext4, default   ext4, no journal
  initial writes   13.0 MB/s        15.4 MB/s          15.7 MB/s
  rewrites         13.1 MB/s        15.6 MB/s          15.9 MB/s
  reads            15.2 MB/s        16.9 MB/s          17.2 MB/s
  re-reads         15.3 MB/s        16.9 MB/s          17.2 MB/s
  random readers    5.6 MB/s         5.6 MB/s           5.7 MB/s
  random writers    5.1 MB/s         5.3 MB/s           5.4 MB/s 

So it seems that, so far, this was a useful exercise.

Signed-off-by: Frank Mayhar <fmayhar@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 63 insertions, 20 deletions

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index c75384b..ad13a84 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -7,53 +7,96 @@
 int __ext4_journal_get_undo_access(const char *where, handle_t *handle,
 				struct buffer_head *bh)
 {
-	int err = jbd2_journal_get_undo_access(handle, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_get_undo_access(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	}
 	return err;
 }
 
 int __ext4_journal_get_write_access(const char *where, handle_t *handle,
 				struct buffer_head *bh)
 {
-	int err = jbd2_journal_get_write_access(handle, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_get_write_access(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	}
 	return err;
 }
 
 int __ext4_journal_forget(const char *where, handle_t *handle,
 				struct buffer_head *bh)
 {
-	int err = jbd2_journal_forget(handle, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_forget(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	}
 	return err;
 }
 
 int __ext4_journal_revoke(const char *where, handle_t *handle,
 				ext4_fsblk_t blocknr, struct buffer_head *bh)
 {
-	int err = jbd2_journal_revoke(handle, blocknr, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_revoke(handle, blocknr, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	}
 	return err;
 }
 
 int __ext4_journal_get_create_access(const char *where,
 				handle_t *handle, struct buffer_head *bh)
 {
-	int err = jbd2_journal_get_create_access(handle, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_get_create_access(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	}
 	return err;
 }
 
-int __ext4_journal_dirty_metadata(const char *where,
-				handle_t *handle, struct buffer_head *bh)
+int __ext4_handle_dirty_metadata(const char *where, handle_t *handle,
+				 struct inode *inode, struct buffer_head *bh)
 {
-	int err = jbd2_journal_dirty_metadata(handle, bh);
-	if (err)
-		ext4_journal_abort_handle(where, __func__, bh, handle, err);
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_dirty_metadata(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	} else {
+		mark_buffer_dirty(bh);
+		if (inode && inode_needs_sync(inode)) {
+			sync_dirty_buffer(bh);
+			if (buffer_req(bh) && !buffer_uptodate(bh)) {
+				ext4_error(inode->i_sb, __func__,
+					   "IO error syncing inode, "
+					   "inode=%lu, block=%llu",
+					   inode->i_ino,
+					   (unsigned long long) bh->b_blocknr);
+				err = -EIO;
+			}
+		}
+	}
 	return err;
 }