4-6 liters might be a bit much, but 3-4 is pretty doable. The Troll frame allows enough space for a water bladder plus some other stuff (e.g. some food), although yours is smaller than mine (I have 18 inch). I have a custom framebag from Greg Wheelwright in Boulder, but you can also get the Revelate ones that already fit the Troll. Also, try making use of extra spots for water bottles - bottle cage on top of the stem, bottle cages hoseclamped onto the fork, bottle cage hoseclamped onto the bottom of the frame.
I love having a framebag. It's perfect for day rides and along with a handlebar roll and, in winter, rear rack with stuff on top, becomes a pretty solid "bikepacking" setup.