[PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

[peterz@infradead.org (Peter Zijlstra)]

On Fri, 2010-08-27 at 17:16 +0900, KAMEZAWA Hiroyuki wrote:
> > How about changing following this?
> > The thing is MAX_ORDER is static. But we want to avoid too big
> > MAX_ORDER of whole zones to support devices which requires big
> > allocation chunk.
> > So let's add MAX_ORDER into each zone and then, each zone can have
> > different max order.
> > For example, while DMA[32], NORMAL, HIGHMEM can have normal size 11,
> > MOVABLE zone could have a 15.
> > 
> > This approach has a big side effect?

The side effect of increasing MAX_ORDER is that page allocations get
more expensive since the buddy tree gets larger, yielding more
splits/merges.

> Hm...need to check hard coded MAX_ORDER usages...I don't think
> side-effect is big. Hmm. But I think enlarging MAX_ORDER isn't an
> important thing. A code which strips contiguous chunks of pages from
> buddy allocator is a necessaty thing, as..

Right, once we can explicitly free the pages we want, crossing MAX_ORDER
isn't too hard like you say, we can simply continue with freeing the
next in order page.