[PATCH] JBD: transaction buffer accounting fix

From: Alex Tomas <bzzz@tmi.comex.ru>

start_this_handle() takes into account t_outstanding_credits when calculating
log free space, but journal_next_log_block() accounts for blocks being logged
also.  Hence, blocks are accounting twice.  This effectively reduces the
amount of log space available to transactions and forces more commits.

Fix it by decrementing t_outstanding_credits each time we allocate a new
journal block.

fs/jbd/commit.c

@@ -401,6 +401,13 @@ void journal_commit_transaction(journal_t *journal)
 			continue;
 		}
 
+		/*
+		 * start_this_handle() uses t_outstanding_credits to determine
+		 * the free space in the log, but this counter is changed
+		 * by journal_next_log_block() also.
+		 */
+		commit_transaction->t_outstanding_credits--;
+
 		/* Bump b_count to prevent truncate from stumbling over
                    the shadowed buffer!  @@@ This can go if we ever get
                    rid of the BJ_IO/BJ_Shadow pairing of buffers. */