On Mon, 1 Oct 2007 13:55:29 -0700 (PDT)
Christoph Lameter <[email protected]> wrote:
> On Sat, 29 Sep 2007, Andrew Morton wrote:
>
> > > atomic allocations. And with SLUB using higher order pages, atomic !0
> > > order allocations will be very very common.
> >
> > Oh OK.
> >
> > I thought we'd already fixed slub so that it didn't do that. Maybe that
> > fix is in -mm but I don't think so.
> >
> > Trying to do atomic order-1 allocations on behalf of arbitray slab caches
> > just won't fly - this is a significant degradation in kernel reliability,
> > as you've very easily demonstrated.
>
> Ummm... SLAB also does order 1 allocations. We have always done them.
>
> See mm/slab.c
>
> /*
> * Do not go above this order unless 0 objects fit into the slab.
> */
> #define BREAK_GFP_ORDER_HI 1
> #define BREAK_GFP_ORDER_LO 0
> static int slab_break_gfp_order = BREAK_GFP_ORDER_LO;
Do slab and slub use the same underlying page size for each slab?
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.
I've never ever before seen reports of page allocation failures in the
radix-tree node allocation code, and that's the bottom line. This is just
a drop-dead must-fix show-stopping bug. We cannot rely upon atomic order-1
allocations succeeding so we cannot use them for radix-tree nodes. Nor for
lots of other things which we have no chance of identifying.
Peter, is this bug -mm only, or is 2.6.23 similarly failing?
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