Re: [patch] SLQB slab allocator

Nick Piggin
2009-02-05T03:19:14Z

On Thursday 05 February 2009 07:09:15 Christoph Lameter wrote:
> On Wed, 4 Feb 2009, Nick Piggin wrote:
> > That's very true, and we touched on this earlier. It is I guess
> > you can say a downside of queueing. But an analogous situation
> > in SLUB would be that lots of pages on the partial list with
> > very few free objects, or freeing objects to pages with few
> > objects in them. Basically SLUB will have to do the extra work
> > in the fastpath.
>
> But these are pages with mostly allocated objects and just a few objects
> free. The SLAB case is far worse: You have N objects on a queue and they
> are keeping possibly N pages away from the page allocator and in those
> pages *nothing* is used.

Periodic queue trimming should prevent this from becoming a big problem.
It will trim away those objects, and so subsequent allocations will come
from new pages and be densely packed. I don't think I've seen a problem
in SLAB reported from this phenomenon, so I'm not too concerned about it
at the moment.