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, 3 insertions, 2 deletions

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index f2a9cf498ec..e7cd488da4b 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -59,7 +59,8 @@ static int finish_range(handle_t *handle, struct inode *inode,
         /*
          * Make sure the credit we accumalated is not really high
          */
-        if (needed && handle->h_buffer_credits >= EXT4_RESERVE_TRANS_BLOCKS) {
+        if (needed && ext4_handle_has_enough_credits(handle,
+                                                EXT4_RESERVE_TRANS_BLOCKS)) {
                 retval = ext4_journal_restart(handle, needed);
                 if (retval)
                         goto err_out;
@@ -229,7 +230,7 @@ static int extend_credit_for_blkdel(handle_t *handle, struct inode *inode)
 {
         int retval = 0, needed;
 
-        if (handle->h_buffer_credits > EXT4_RESERVE_TRANS_BLOCKS)
+        if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
                 return 0;
         /*
          * We are freeing a blocks. During this we touch