Re: Page allocator: Single Zone optimizations

Andrew Morton
2006-11-01T20:34:51Z

On Wed, 1 Nov 2006 18:26:05 +0000
mel@skynet.ie (Mel Gorman) wrote:

> I never really got this objection. With list-based anti-frag, the
> zone-balancing logic remains the same. There are patches from Andy
> Whitcroft that reclaims pages in contiguous blocks, but still with the same
> zone-ordering. It doesn't affect load balancing between zones as such.

I do believe that lumpy-reclaim (initiated by Andy, redone and prototyped
by Peter, cruelly abandoned) is a perferable approach to solving the
fragmentation approach.

And with __GFP_EASYRECLAIM (please - I just renamed it ;)) (or using
__GFP_HIGHMEM for the same thing) then some of the core lumpy-reclaim
algorithm can be reused for hot-unplug.

If you want to unplug a range of memory then it has to be in a zone which
is 100% __GFP_EASY_RECLAIM (actually the name is still wrong. It should
just be __GFP_RECLAIMABLE).

The hot-unplug code will go through those pages and it will, with 100%
reliability, rip those pages out of the kernel via various means. I think
this can all be done.

And hot-unplug isn't actually the interesting application. Modern Intel
memory controllers apparently have (or will have) the ability to power down
DIMMs.