How can I use all available RAM instead of limited RAM?

I got an email stating "Out of memory: The process "mysqld" was terminated because the system is low on memory." My server has 16GB RAM but according to this mail it's just 3.36 GB. But my hosting provider re-confirmed it's 16GB. Also my server had lots of free memory at the time of "mysqld" termination, Please tell me how to increase the memory level of "mysqld" termination. Email information given below: Out of memory: The process "mysqld" was terminated because the system is low on memory. In order to avoid a system crash due to low memory, the kernel terminated the process named "mysqld" with the PID "1264". Status: Out of Memory Memory Information Used 3.36 GB Available 12.14 GB Installed 15.51 GB My Server's MySQL configuration (my.cnf) as follows: [mysqld] performance-schema = 0 log-error = /var/lib/mysql/coollanding.onlanka.com.err innodb_log_file_size = 4G innodb_buffer_pool_size = 8G innodb_buffer_pool_instances = 9 innodb_file_per_table = 1 max_connections = 1000 max_allowed_packet = 256M innodb_rollback_on_timeout = 1 [mysqld_safe] open_files_limit = 40000