just comment changes and line formatting changes.

storage/maria/checkpoint.c:
  comments
storage/maria/least_recently_dirtied.c:
  comments
storage/maria/ma_check.c:
  line formatting changes neglected from my last merge
storage/maria/ma_ft_parser.c:
  it reduces the diff of MyISAM vs Maria :)
storage/maria/recovery.c:
  comments

storage/maria/checkpoint.c

@@ -46,7 +46,8 @@ CHECKPOINT_LEVEL synchronous_checkpoint_in_progress= NONE;
 
 /*
   Used by MySQL client threads requesting a checkpoint (like "ALTER MARIA
-  ENGINE DO CHECKPOINT"), and probably by maria_panic().
+  ENGINE DO CHECKPOINT"), and probably by maria_panic(), and at the end of the
+  UNDO recovery phase.
 */
 my_bool execute_synchronous_checkpoint(CHECKPOINT_LEVEL level)
 {
@@ -342,8 +343,6 @@ log_write_record(...)
   (requestor does not wait for completion, and does not even later check the
   result).
   In real life it will be called by log_write_record().
-  which explicitely wants to do checkpoint (ALTER ENGINE CHECKPOINT
-  checkpoint_level).
 */
 void request_asynchronous_checkpoint(CHECKPOINT_LEVEL level);
 {
@@ -359,7 +358,8 @@ void request_asynchronous_checkpoint(CHECKPOINT_LEVEL level);
       MAX_LOG_BYTES_WRITTEN_BETWEEN_CHECKPOINTS is passed), so it may not be a
       good idea for each of them to broadcast a cond to wake up the background
       checkpoint thread. We just don't broacast a cond, the checkpoint thread
-      will notice our request in max a few seconds.
+      (see least_recently_dirtied.c) will notice our request in max a few
+      seconds.
     */
     checkpoint_request= level; /* post request */
   }

storage/maria/least_recently_dirtied.c

@@ -181,7 +181,15 @@ flush_one_group_from_LRD()
   */
 }
 
-/* flushes all page from LRD up to approximately rec_lsn>=max_lsn */
+/*
+  Flushes all page from LRD up to approximately rec_lsn>=max_lsn.
+  This is approximate because we flush groups, and because the LRD list may
+  not be exactly sorted by rec_lsn (because for a big row, all pages of the
+  row are inserted into the LRD with rec_lsn being the LSN of the REDO for the
+  first page, so if there are concurrent insertions, the last page of the big
+  row may have a smaller rec_lsn than the previous pages inserted by
+  concurrent inserters).
+*/
 int flush_all_LRD_to_lsn(LSN max_lsn)
 {
   lock(global_LRD_mutex);
@@ -191,7 +199,9 @@ int flush_all_LRD_to_lsn(LSN max_lsn)
   {
     if (flush_one_group_from_LRD()) /* will unlock LRD mutex */
       return 1;
-    /* scheduler may preempt us here so that we don't take full CPU */
+    /*
+      The scheduler may preempt us here as we released the mutex; this is good.
+    */
     lock(global_LRD_mutex);
   }
   unlock(global_LRD_mutex);

storage/maria/ma_check.c

@@ -460,8 +460,8 @@ int maria_chk_key(HA_CHECK *param, register MARIA_HA *info)
       auto_increment= ma_retrieve_auto_increment(info, info->rec_buff);
       if (auto_increment > info->s->state.auto_increment)
       {
-	_ma_check_print_warning(param,
-			       "Auto-increment value: %s is smaller than max used value: %s",
+	_ma_check_print_warning(param, "Auto-increment value: %s is smaller "
+                                "than max used value: %s",
                                 llstr(info->s->state.auto_increment,buff2),
                                 llstr(auto_increment, buff));
       }
@@ -481,8 +481,8 @@ int maria_chk_key(HA_CHECK *param, register MARIA_HA *info)
       {
 	/* Don't count this as a real warning, as mariachk can't correct it */
 	uint save=param->warning_printed;
-	_ma_check_print_warning(param,
-			       "Found row where the auto_increment column has the value 0");
+	_ma_check_print_warning(param, "Found row where the auto_increment "
+                                "column has the value 0");
 	param->warning_printed=save;
       }
       maria_extra(info,HA_EXTRA_NO_KEYREAD,0);
@@ -1165,7 +1165,8 @@ int maria_chk_data_link(HA_CHECK *param, MARIA_HA *info,int extend)
                            SEARCH_SAME, info->s->state.key_root[key]);
               if (search_result)
               {
-                _ma_check_print_error(param,"Record at: %10s  Can't find key for index: %2d",
+                _ma_check_print_error(param,"Record at: %10s  "
+                                      "Can't find key for index: %2d",
                                       llstr(start_recpos,llbuff),key+1);
                 if (error++ > MAXERR || !(param->testflag & T_VERBOSE))
                   goto err2;

storage/maria/ma_ft_parser.c

@@ -204,8 +204,8 @@ byte maria_ft_simple_get_word(CHARSET_INFO *cs, byte **start, const byte *end,
                         FT_WORD *word, my_bool skip_stopwords)
 {
   byte *doc= *start;
-  int ctype;
   uint mwc, length, mbl;
+  int ctype;
   DBUG_ENTER("maria_ft_simple_get_word");
 
   do

storage/maria/recovery.c

@@ -221,10 +221,6 @@ int recovery()
   /*
     mark that checkpoint requests are now allowed.
   */
-  /*
-    when all rollback threads have terminated, somebody should print "rollback
-    finished" to the error log.
-  */
 }
 
 pthread_handler_decl rollback_background_thread()
@@ -248,13 +244,7 @@ pthread_handler_decl rollback_background_thread()
   {
     /*
       All rollback threads are done.  Print "rollback finished" to the error
-      log.  The UNDO phase has the reputation of being a slow operation
-      (slower than the REDO phase), so taking a checkpoint at the end of it is
-      intelligent, but as this UNDO phase generates REDOs and CLR_ENDs, if it
-      did a lot of work then the "automatic checkpoint when much has been
-      written to the log" will do it; and if the UNDO phase didn't do a lot of
-      work, no need for a checkpoint. If we change our mind and want to force
-      a checkpoint at the end of the UNDO phase, simply call it here.
+      log and take a full checkpoint.
     */
   }
   unlock_mutex(rollback_threads);