Install DragonFlyBSD on 48 MB RAM

[Matthew Dillon]

:One of our developers tested with snapshots; it looks like the DMA
:reserve commit is the one that made DF no longer run w/ 48MB. That
:makes sense, as 16MB of physical memory is locked up by that commit.
:You should be able to boot with a loader variable set to reserve less
:physical memory.
:
:We someday need a better physmem allocator; the 16MB reserve is a good
:step, but a low-fragmentation allocator would be better.
:
:-- vs;

   It should be reserving less space on low-memory machines.

        if (vm_dma_reserved == 0) {
                vm_dma_reserved = 16 * 1024 * 1024;     /* 16MB */
                if (vm_dma_reserved > total / 16)
                        vm_dma_reserved = total / 16;
        }

   We could try zeroing it.  Or perhaps the calculation is wrong...
   maybe it should be basing the test on 'npages' instead of 'total'.
   e.g. ((vm_paddr_t)npages * PAGE_SIZE / 16) instead of (total / 16).

   However, we really don't support machines with so little memory,
   even if the thing manages to boot.  If a simple change makes it work
   then fine, but otherwise I'm skeptical of the value.

   This variable is a tunable.  Try setting 'vm.dma_reserved=0' in the
   boot loader.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>