Re: [PATCH] Tight check of pfn_valid on sparsemem - v4

From: Christoph Lameter
Date: Fri Jul 30 2010 - 08:48:14 EST

On Thu, 29 Jul 2010, Dave Hansen wrote:

> SPARSEMEM_EXTREME would be a bit different. It's a 2-level lookup.
> You'd have 16 "section roots", each representing 256MB of address space.
> Each time we put memory under one of those roots, we'd fill in a
> 512-section second-level table, which is designed to always fit into one
> page. If you start at 256MB, you won't waste all those entries.

That is certain a solution to the !MMU case and it would work very much
like a page table. If you have an MMU then the vmemmap sparsemem
configuration can take advantage of of that to avoid the 2 level lookup.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at