On Thu, 2010-08-26 at 04:40 +0200, Micha? Nazarewicz wrote:

I think that the biggest problem is fragmentation here.  For instance,
I think that a situation where there is enough free space but it's
fragmented so no single contiguous chunk can be allocated is a serious
problem.  However, I would argue that if there's simply no space left,
a multimedia device could fail and even though it's not desirable, it
would not be such a big issue in my eyes.

So, if only movable or discardable pages are allocated in CMA managed
regions all should work well.  When a device needs memory discardable
pages would get freed and movable moved unless there is no space left
on the device in which case allocation would fail. 

If you'd actually looked at the page allocator you'd see its capable of
doing exactly that!

I has the notion of movable pages, it can defragment free space (called
compaction).

Use it!