Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 1 Oct 2007 14:38:55 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> On Mon, 1 Oct 2007, Andrew Morton wrote:
> 
> > Do slab and slub use the same underlying page size for each slab?
> 
> SLAB cannot pack objects as dense as SLUB and they have different 
> algorithm to make the choice of order. Thus the number of objects per slab 
> may vary between SLAB and SLUB and therefore also the choice of order to 
> store these objects.
> 
> > Single data point: the CONFIG_SLAB boxes which I have access to here are
> > using order-0 for radix_tree_node, so they won't be failing in the way in
> > which Peter's machine is.
> 
> Upstream SLUB uses order 0 allocations for the radix tree.

OK, that's a relief.

> MM varies 
> because the use of higher order allocs is more loose if the mobility 
> algorithms are found to be active:
> 
> 2.6.23-rc8:
> 
> Name                   Objects Objsize    Space Slabs/Part/Cpu  O/S O %Fr %Ef Flg\
> radix_tree_node          14281     552     9.9M     2432/948/1    7 0  38  79

Ah.  So the already-dropped
slub-exploit-page-mobility-to-increase-allocation-order.patch was the
culprit?