Discoveryd & LaunchServicesd Huge Memory Consumption
This is a known issue in Yosemite, although it doesn't affect everyone - I have 5 Macs running Yosemite and one suffers badly, but the others not at all.

Temporary relief comes from rebooting or stopping and restarting the affected services. For discoveryd, in Terminal, do:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist

Launchervicesd may respond to the same commands - I don't have any experience of that