Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

Linus Torvalds
2005-11-03T18:09:05Z

On Thu, 3 Nov 2005, Arjan van de Ven wrote:

> On Thu, 2005-11-03 at 09:51 -0800, Martin J. Bligh wrote:
>
> > For amusement, let me put in some tritely oversimplified math. For the
> > sake of arguement, assume the free watermarks are 8MB or so. Let's assume
> > a clean 64-bit system with no zone issues, etc (ie all one zone). 4K pages.
> > I'm going to assume random distribution of free pages, which is
> > oversimplified, but I'm trying to demonstrate a general premise, not get
> > accurate numbers.
>
> that is VERY over simplified though, given the anti-fragmentation
> property of buddy algorithm

Indeed. I write a program at one time doing random allocation and
de-allocation and looking at what the output was, and buddy is very good
at avoiding fragmentation.

These days we have things like per-cpu lists in front of the buddy
allocator that will make fragmentation somewhat higher, but it's still
absolutely true that the page allocation layout is _not_ random.

Linus