Fiasco.OC Kernel memory running out (I think)

Hi, I'm using Fiasco.OC r56 on x86_64 (with Genode). After doing quite a lot of memory mapping, mem_map finally fails. It seems that the _allocators[0]->alloc(...) fails during the Mapping_tree::new operator creation of a Mapping_tree object in the Treemap::tree method. How can I increase the available kernel memory attached to this allocator? Thanks Daniel