Where and how to fix the config so that mysql does not fall?

Question

MySQL

Periodically falls north, the last week very often.
Here are the last lines from the log

170128 19:38:09 InnoDB: Initializing buffer pool, size = 128.0M
InnoDB: mmap(137363456 bytes) failed; errno 12
170128 19:38:09 InnoDB: Completed initialization of buffer pool
170128 19:38:09 InnoDB: Fatal error: cannot allocate memory for the buffer pool
170128 19:38:09 [ERROR] Plugin 'InnoDB' init function returned error.
170128 19:38:09 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
170128 19:38:09 [ERROR] Unknown/unsupported storage engine: InnoDB
170128 19:38:09 [ERROR] Aborting

170128 19:38:09 [Note] /usr/sbin/mysqld: Shutdown complete

As I understand it, there is not enough RAM, tell me who had it, where to fix it so as not to break everything, there are a couple of dozen working sites on the server. I will be grateful

Answer 1

https://www.digitalocean.com/community/questions/m...
Shortly: add (or replace existing line) to the /etc/mysql/my.cnf :
This will decrease mysql requirements.
And here is the original answer (with explanations):
stackoverflow.com/a/12683951/1115187
Another approaches to solve the problem:
askubuntu.com/a/457932/400409
0 google link

Answer 2

By the way, sometimes MySQL is set up fine, but it crashes because PHP-FPM eats too much.
In such cases, it is worth fixing its configs a little.