On 21 Aug 2025, at 16:06, David Hildenbrand wrote:
In an ideal world, we wouldn't have to deal with SPARSEMEM without SPARSEMEM_VMEMMAP, but in particular for 32bit SPARSEMEM_VMEMMAP is considered too costly and consequently not supported.
However, if an architecture does support SPARSEMEM with SPARSEMEM_VMEMMAP, let's forbid the user to disable VMEMMAP: just like we already do for arm64, s390 and x86.
So if SPARSEMEM_VMEMMAP is supported, don't allow to use SPARSEMEM without SPARSEMEM_VMEMMAP.
This implies that the option to not use SPARSEMEM_VMEMMAP will now be gone for loongarch, powerpc, riscv and sparc. All architectures only enable SPARSEMEM_VMEMMAP with 64bit support, so there should not really be a big downside to using the VMEMMAP (quite the contrary).
This is a preparation for not supporting
(1) folio sizes that exceed a single memory section (2) CMA allocations of non-contiguous page ranges
in SPARSEMEM without SPARSEMEM_VMEMMAP configs, whereby we want to limit possible impact as much as possible (e.g., gigantic hugetlb page allocations suddenly fails).
Sounds like a good idea.
Cc: Huacai Chen chenhuacai@kernel.org Cc: WANG Xuerui kernel@xen0n.name Cc: Madhavan Srinivasan maddy@linux.ibm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Albert Ou aou@eecs.berkeley.edu Cc: Alexandre Ghiti alex@ghiti.fr Cc: "David S. Miller" davem@davemloft.net Cc: Andreas Larsson andreas@gaisler.com Signed-off-by: David Hildenbrand david@redhat.com
mm/Kconfig | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
Acked-by: Zi Yan ziy@nvidia.com
Best Regards, Yan, Zi