linux – The system uses almost all my RAM

I'm using an Ubuntu Linux distribution (17.10) and my system specifications are

Memory: 7.6 gio
Processor: Intel® Core ™ i5-3210M Processor 2.50 GHz × 4
Graphics: Intel® Ivybridge Mobile
GNOME: 3.26.2
Type of operating system: 64 bits
Disk: 768.7 GB

Currently I have Tilix, Chrome (<6 tabs), PhpStorm open.
and watch npm compile my code on the go.

My use of the system are now

Memory 87% = 6.62 / 7.6GiB
Swap 15% = 1.13 / 7.30Gib

I've joined screen capture from htop.
What could be the reason for the use of resources?

Screen capture