Re: [RFC] Remove unswappable anonymous pages off the LRU

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 15 Feb 2007 21:25:53 -0800 (PST) Christoph Lameter <clameter@sgi.com> wrote:

> On Thu, 15 Feb 2007, Andrew Morton wrote:
> 
> > hm.  We can calculate page_zone(page) from the pfn.  And I suspect we can
> > do that locklessly too.  I bet a nice tight implementation of that would be
> > efficient enough and it'll reclaim heaps of flags.
> 
> You mean encode the node and the zone_id in the pfn?

Maybe.  Or just leave the pfns as they are and implement a decent lookup
algorithm.

For a pc it'd be something like

	for (i = ZONE_DMA; i <= ZONE_HIGHMEM; i++) {
		if (pfn >= first_pfn(i) && pfn <= last_pfn(i))
			success();
	}

if you get my drift.

I dunno how complex that would get in the worst cases.

> Ummm... That would 
> get us into lots of trouble with pfn_to_page and friends.
> 
> The sparsemem section field could be available. A virtual 
> memmap based implementation would not need the section number and would 
> get rid of the sparsemem table lookups.Problem is that we cannot do it on 
> 32 bit platforms because of the lack of virtual memory.

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