> Could kernel use virtual memory hardware to make non-linear chunks of
> memory to look linear? It seems to me that it could solve the problems
> with memory fragmentation and DMA memory allocation.
>
> DMA memory could be allocated by moving allocated blocks away from the
> lower 16MB, and other parts of kernel could be made happy by changing the
> page tables accordingly.
>
> So, is this possible/feasible/too ugly to implement?
Yes it's possible, and yes people are working on it (both myself and Mark
Hemment are doing similar, but different implementations). However we do
generally want to avoid these sorts of memory management tricks as
otherwise one's system might end up spending a great deal of time
shuffling pages around in memory. Any driver that needs to regularly
allocate dmable pages should really think about doing that at startup,
and just holding onto these flip buffers for its lifetime.
-ben