What I did before the disaster was:
innodb_buffer_pool_size=4G innodb_buffer_pool_instance=2 innodb_read_io_threads=12 innodb_write_io_threads=12 innodb_io_capacity=300 innodb_log_file_size=128M
and after that
$ service mysql stop $ cd /var/lib/mysql $ rm -f ibdata1 ib_logfile* $ service mysql start
ERROR 1146 (42S02): Table 'db.table' doesn't exist for every table.
My site is down, database backup does not help.