On Mon, 2007-10-01 at 14:30 -0700, Andrew Morton wrote:
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> On Mon, 1 Oct 2007 13:55:29 -0700 (PDT)
> Christoph Lameter <clameter@sgi.com> wrote:
>=20
> > On Sat, 29 Sep 2007, Andrew Morton wrote:
> >=20
> > > > atomic allocations. And with SLUB using higher order pages, atomic =
!0
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> > > > order allocations will be very very common.
> > >=20
> > > Oh OK.
> > >=20
> > > I thought we'd already fixed slub so that it didn't do that.  Maybe t=
hat
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> > > fix is in -mm but I don't think so.
> > >=20
> > > Trying to do atomic order-1 allocations on behalf of arbitray slab ca=
ches
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> > > just won't fly - this is a significant degradation in kernel reliabil=
ity,
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> > > as you've very easily demonstrated.
> >=20
> > Ummm... SLAB also does order 1 allocations. We have always done them.
> >=20
> > See mm/slab.c
> >=20
> > /*
> >  * 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 =3D BREAK_GFP_ORDER_LO;
>=20
> Do slab and slub use the same underlying page size for each slab?
>=20
> 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.
>=20
> 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 jus=
t
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> a drop-dead must-fix show-stopping bug.  We cannot rely upon atomic order=
-1
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> allocations succeeding so we cannot use them for radix-tree nodes.  Nor f=
or
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> lots of other things which we have no chance of identifying.
>=20
> Peter, is this bug -mm only, or is 2.6.23 similarly failing?

I'm mainly using -mm (so you have at least one tester :-), I think the
-mm specific SLUB patch that ups slub_min_order makes the problem -mm
specific, would have to test .23.