Re: [RFC] Make the slab allocator observe NUMA policies

[Andi Kleen <ak@suse.de>]

On Monday 14 November 2005 19:05, Christoph Lameter wrote:
> On Sun, 13 Nov 2005, Andi Kleen wrote:
> 
> > On Friday 11 November 2005 18:40, Christoph Lameter wrote:
> > 
> > > Hmm. Thats not easy to do since the slab allocator is managing the pages 
> > > in terms of the nodes where they are located. The whole thing is geared to 
> > > first inspect the lists for one node and then expand if no page is 
> > > available.
> > 
> > Yes, that's fine - as long as it doesn't allocate too many 
> > pages at one go (which it doesn't) then the interleaving should
> > even the allocations out at page level.
> 
> The slab allocator may allocate pages higher orders which need to 
> be physically continuous. 

> Any idea how to push this to the page allocation within the slab without 
> rearchitecting the thing?

I believe that's only a small fraction of the allocations, for where
the slabs are big enough to be an significant part of the page.

Proof: VM breaks down with higher orders. If slab would use them
all the time it would break down too. It doesn't. Q.E.D ;-)

Also looking at the objsize colum in /proc/slabinfo most slabs are
significantly smaller than a page and the higher kmalloc slabs don't have 
too many objects, so slab shouldn't do this too often.

You're right they're a problem, but perhaps they can be just ignored
(like if they are <20% of the allocations the inbalance resulting
from them might not be too bad)

Another way (as a backup option) would be to RR them as higher order pages, 
but that would need new special code.

-Andi

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