To tune properly, Ive used a nice perl script to calculate out per thread memory usage; Yours reads as follows;
/usr/local/mysql5021/bin/mysqld will use at most:
42.0 MB for global stuff
10.5 MB per thread
10.3 GB total (with 1000 active threads)
and additionally:
16.0 MB for each HEAP table
16.0 MB for each temporary table
See the forge;
http://forge.mysql.com/snippets/view.php?id=44
Dont know if that may trigger something for you? Your ndb_mgmd should be logging somewhere; config.ini under [NDB_MGMD] see your LogDestination parameter. See if anything is in that at all. Otherwise it could just by mysqld using all your memory.
When the problem occurs, in linux use the command 'free' to see your memory status. Provide that here perhaps.
Adam