Re: NUMA policy issues with ZONE_MOVABLE

[Christoph Lameter <clameter@sgi.com>]

On Thu, 26 Jul 2007, Mel Gorman wrote:

> > How about changing __alloc_pages to lookup the zonelist on its own based 
> > on a node parameter and a set of allowed nodes? That may significantly 
> > clean up the memory policy layer and the cpuset layer. But it will 
> > increase the effort to scan zonelists on each allocation. A large system 
> > with 1024 nodes may have more than 1024 zones on each nodelist!
> > 
> 
> That sounds like it would require the creation of a zonelist for each
> allocation attempt. That is not ideal as there is no place to allocate
> the zonelist during __alloc_pages(). It's not like it can call
> kmalloc().

Nope it would just require scanning the full zonelists on every alloc as 
you already propose.

> > Nope it would not fail. NUMAQ has policy_zone == HIGHMEM and slab 
> > allocations do not use highmem.
> 
> It would fail if policy_zone didn't exist, that was my point. Without
> policy_zone, we apply policy to all allocations and that causes
> problems.

policy_zone can not exist due to ZONE_DMA32 ZONE_NORMAL issues. See my 
other email.


> I ran the patch on a wide variety of machines, NUMA and non-NUMA. The
> non-NUMA machines showed no differences as you would expect for
> kernbench and aim9. On NUMA machines, I saw both small gains and small
> regressions. By and large, the performance was the same or within 0.08%
> for kernbench which is within noise basically.

Sound okay.

> It might be more pronounced on larger NUMA machines though, I cannot
> generate those figures.

I say lets go with the filtering. That would allow us to also catch other 
issues that are now developing on x86_64 with ZONE_NORMAL and ZONE_DMA32.
 
> I'll try adding a should_filter to zonelist that is only set for
> MPOL_BIND and see what it looks like.

Maybe that is not worth it.

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