increased used memory but no process's memory is increasing

[hawk hsieh]

Hi:

I have a service that run on google compute engine. Overtime, the used memory is getting large until exhausted.

How can I do to avoid the memory continue clime to 100% ? 

This is the memory of all process. As picture, no process has the getting large pattern. 

I figure out the used memory is increased overtime(purple area).

Thus, the used memory has a slope.