On Fri, Aug 29, 2025 at 01:57:22PM +0200, David Hildenbrand wrote: > On 28.08.25 17:10, Lorenzo Stoakes wrote: > > On Thu, Aug 28, 2025 at 12:01:15AM +0200, David Hildenbrand wrote: > > > Let's limit the maximum folio size in problematic kernel config where > > > the memmap is allocated per memory section (SPARSEMEM without > > > SPARSEMEM_VMEMMAP) to a single memory section. > > > > > > Currently, only a single architectures supports ARCH_HAS_GIGANTIC_PAGE > > > but not SPARSEMEM_VMEMMAP: sh. > > > > > > Fortunately, the biggest hugetlb size sh supports is 64 MiB > > > (HUGETLB_PAGE_SIZE_64MB) and the section size is at least 64 MiB > > > (SECTION_SIZE_BITS == 26), so their use case is not degraded. > > > > > > As folios and memory sections are naturally aligned to their order-2 size > > > in memory, consequently a single folio can no longer span multiple memory > > > sections on these problematic kernel configs. > > > > > > nth_page() is no longer required when operating within a single compound > > > page / folio. > > > > > > Reviewed-by: Zi Yan <z...@nvidia.com> > > > Acked-by: Mike Rapoport (Microsoft) <r...@kernel.org> > > > Signed-off-by: David Hildenbrand <da...@redhat.com> > > > > Realy great comments, like this! > > > > I wonder if we could have this be part of the first patch where you fiddle > > with MAX_FOLIO_ORDER etc. but not a big deal. > > I think it belongs into this patch where we actually impose the > restrictions.
Sure it's not a big deal. > > [...] > > > > +/* > > > + * Only pages within a single memory section are guaranteed to be > > > + * contiguous. By limiting folios to a single memory section, all folio > > > + * pages are guaranteed to be contiguous. > > > + */ > > > +#define MAX_FOLIO_ORDER PFN_SECTION_SHIFT > > > > Hmmm, was this implicit before somehow? I mean surely by the fact as you say > > that physical contiguity would not otherwise be guaranteed :)) > > Well, my patches until this point made sure that any attempt to use a larger > folio would fail in a way that we could spot now if there is any offender. Ack yeah. > > That is why before this change, nth_page() was required within a folio. > > Hope that clarifies it, thanks! Yes thanks! :) > > -- > Cheers > > David / dhildenb > Cheers, Lorenzo
