Re: [patch] SLQB slab allocator

Nick Piggin
2009-02-03T01:54:09Z

On Tuesday 27 January 2009 04:28:03 Christoph Lameter wrote:
> n Fri, 23 Jan 2009, Nick Piggin wrote:
> > According to memory policies, a task's memory policy is supposed to
> > apply to its slab allocations too.
>
> It does apply to slab allocations. The question is whether it has to apply
> to every object allocation or to every page allocation of the slab
> allocators.

Quite obviously it should. Behaviour of a slab allocation on behalf of
some task constrained within a given node should not depend on the task
which has previously run on this CPU and made some allocations. Surely
you can see this behaviour is not nice.

> > > Memory policies are applied in a fuzzy way anyways. A context switch
> > > can result in page allocation action that changes the expected
> > > interleave pattern. Page populations in an address space depend on the
> > > task policy. So the exact policy applied to a page depends on the task.
> > > This isnt an exact thing.
> >
> > There are other memory policies than just interleave though.
>
> Which have similar issues since memory policy application is depending on
> a task policy and on memory migration that has been applied to an address
> range.

What similar issues? If a task ask to have slab allocations constrained
to node 0, then SLUB hands out objects from other nodes, then that's bad.

> > But that is wrong. The lists obviously have high water marks that
> > get trimmed down. Periodic trimming as I keep saying basically is
> > alrady so infrequent that it is irrelevant (millions of objects
> > per cpu can be allocated anyway between existing trimming interval)
>
> Trimming through water marks and allocating memory from the page allocator
> is going to be very frequent if you continually allocate on one processor
> and free on another.

Um yes, that's the point. But you previously claimed that it would just
grow unconstrained. Which is obviously wrong. So I don't understand what
your point is.