On Thu, Feb 25, 2021 at 07:38:44PM +0100, Vlastimil Babka wrote:

On 2/25/21 7:05 PM, Mike Rapoport wrote:

quoted

quoted

What if two zones are adjacent? I.e. if the hole was at a boundary between two
zones.

What do you mean by "adjacent zones"? If there is a hole near the zone
boundary, zone span would be clamped to exclude the hole.

Yeah, zone span should exclude those pages, but you still somehow handle them?
That's how I read "pages that are not spanned by any node will get links to the
adjacent zone/node."
So is it always a unique zone/node can be determined?

Let's say we have:

<memory on node 0>
---- pageblock boundary ----
<more memory on node 0>
<a hole>
<memory on node 1>
---- pageblock boundary ----

Now I hope such configurations don't really exist :) But if we simulated them in
QEMU, what would be the linkage in struct pages in that hole?

I don't think such configuration is possible in practice but it can be
forced with e.g memmap="2M hole at 4G - 1M".

The hole in your example the hole will get node1 for node and zone that
spans the beginning of node1 for zone.
 
-- 
Sincerely yours,
Mike.