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, 9 insertions, 8 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 7beab7141dd..edb512b2ec4 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2553,7 +2553,8 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
 	ext4_mb_init_per_dev_proc(sb);
 	ext4_mb_history_init(sb);
 
-	sbi->s_journal->j_commit_callback = release_blocks_on_commit;
+	if (sbi->s_journal)
+		sbi->s_journal->j_commit_callback = release_blocks_on_commit;
 
 	printk(KERN_INFO "EXT4-fs: mballoc enabled\n");
 	return 0;
@@ -2854,7 +2855,7 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 		mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group),
 				bitmap_bh->b_data, ac->ac_b_ex.fe_start,
 				ac->ac_b_ex.fe_len);
-		err = ext4_journal_dirty_metadata(handle, bitmap_bh);
+		err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 		if (!err)
 			err = -EAGAIN;
 		goto out_err;
@@ -2901,10 +2902,10 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 		spin_unlock(sb_bgl_lock(sbi, flex_group));
 	}
 
-	err = ext4_journal_dirty_metadata(handle, bitmap_bh);
+	err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 	if (err)
 		goto out_err;
-	err = ext4_journal_dirty_metadata(handle, gdp_bh);
+	err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
 
 out_err:
 	sb->s_dirt = 1;
@@ -4414,7 +4415,7 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
 	struct rb_node **n = &db->bb_free_root.rb_node, *node;
 	struct rb_node *parent = NULL, *new_node;
 
-
+	BUG_ON(!ext4_handle_valid(handle));
 	BUG_ON(e4b->bd_bitmap_page == NULL);
 	BUG_ON(e4b->bd_buddy_page == NULL);
 
@@ -4600,7 +4601,7 @@ do_more:
 
 	/* We dirtied the bitmap block */
 	BUFFER_TRACE(bitmap_bh, "dirtied bitmap block");
-	err = ext4_journal_dirty_metadata(handle, bitmap_bh);
+	err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 
 	if (ac) {
 		ac->ac_b_ex.fe_group = block_group;
@@ -4609,7 +4610,7 @@ do_more:
 		ext4_mb_store_history(ac);
 	}
 
-	if (metadata) {
+	if (metadata && ext4_handle_valid(handle)) {
 		/* blocks being freed are metadata. these blocks shouldn't
 		 * be used until this transaction is committed */
 		ext4_mb_free_metadata(handle, &e4b, block_group, bit, count);
@@ -4639,7 +4640,7 @@ do_more:
 
 	/* And the group descriptor block */
 	BUFFER_TRACE(gd_bh, "dirtied group descriptor block");
-	ret = ext4_journal_dirty_metadata(handle, gd_bh);
+	ret = ext4_handle_dirty_metadata(handle, NULL, gd_bh);
 	if (!err)
 		err = ret;