Re: [PATCH 04/10] mm: slub: add knowledge of reserve pages

Christoph Lameter
2007-08-20T19:26:20Z

On Mon, 20 Aug 2007, Pekka Enberg wrote:

> Hi Peter,
>
> On Mon, 2007-08-20 at 12:12 +0300, Pekka J Enberg wrote:
> > > Any reason why the callers that are actually interested in this don't do
> > > page->reserve on their own?
>
> On 8/20/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> > because new_slab() destroys the content?
>
> Right. So maybe we could move the initialization parts of new_slab()
> to __new_slab() so that the callers that are actually interested in
> 'reserve' could do allocate_slab(), store page->reserve and do rest of
> the initialization with it?

I am still not convinced about this approach and there seems to be
agreement that this is not working on large NUMA. So #ifdef it out?
!CONFIG_NUMA? Some more general approach that does not rely on a single
slab being a reserve?

The object is to check the alloc flags when having allocated a reserve
slab right? Adding another flag SlabReserve and keying off on that one may
be the easiest solution.

I have pending patches here that add per cpu structures. Those will make
that job easier.

> As for the __GFP_WAIT handling, I *think* we can move the interrupt
> enable/disable to allocate_slab()... Christoph?

The reason the enable/disable is in new_slab is to minimize interrupt
holdoff time. If we move it to allocate slab then the slab preparation is
done with interrupts disabled.