bhyve memory should exert memory pressure
When bhyve allocates memory for a guest (for the guest RAM, specifically) today, it does so in a
KM_NOSLEEP manner. This is to avoid the allocation entering an uninterruptable (by signals) sleep, but also results in the allocation bypassing logic which informs the rest of the system about the memory pressure exerted by the allocation. In order to make timely and reliable allocations, those page reservation mechanisms should be updated to allow requests which can apply that memory pressure (implying KM_SLEEP), but are also fallible and interruptable via signal, so that bhyve may be updated to use them.