On 2/25/21 7:05 PM, Mike Rapoport wrote: > On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote: >> > >> > unset zone link in struct page will trigger >> > >> > VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); >> >> ... in set_pfnblock_flags_mask() when called with a struct page from the >> "Unknown E820 type" range. > > "... in set_pfnblock_flags_mask() when called with a struct page from a range > other than E820_TYPE_RAM" > > then :) Better :) >> > because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link >> > in struct page) in the same pageblock. >> >> I would say "there are apparently pages" ... "and ZONE_DMA does not span this range" > > I'd rephrase it differently, something like > > "because there are pages in the range of ZONE_DMA32 but the unset zone link > in struct page makes them appear as a part of ZONE_DMA" Much better, thanks! >> > Interleave initialization of the unavailable pages with the normal >> > initialization of memory map, so that zone and node information will be >> > properly set on struct pages that are not backed by the actual memory. >> > >> > With this change the pages for holes inside a zone will get proper >> > zone/node links and the pages that are not spanned by any node will get >> > links to the adjacent zone/node. >> >> 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?
