+ loongarch-mm-disable-device-dax-vmemmap-optimization.patch added to mm-new branch

+ loongarch-mm-disable-device-dax-vmemmap-optimization.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: loongarch/mm: disable device DAX vmemmap optimization
has been added to the -mm mm-new branch.  Its filename is
     loongarch-mm-disable-device-dax-vmemmap-optimization.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/loongarch-mm-disable-device-dax-vmemmap-optimization.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: loongarch/mm: disable device DAX vmemmap optimization
Date: Sat, 07 Nov 2026 12:31:20 +0800

LoongArch selects ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP but not
ARCH_WANT_OPTIMIZE_DAX_VMEMMAP. Its vmemmap_free() implementation is also
empty, so it cannot tear down optimized Device DAX mappings.

A later change removes the generic Device DAX architecture gate and lets
vmemmap_populate() decide whether a section can use optimization. Clear the
section compound order in the LoongArch path so Device DAX keeps using
unoptimized mappings.

This does not affect HugeTLB HVO: LoongArch does not support gigantic
pages, so HugeTLB does not use section-based vmemmap optimization there.

Link: https://lore.kernel.org/20261107043122.25650-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <chleroy@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
---

 arch/loongarch/mm/init.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/loongarch/mm/init.c~loongarch-mm-disable-device-dax-vmemmap-optimization
+++ a/arch/loongarch/mm/init.c
@@ -15,6 +15,7 @@
 #include <linux/memblock.h>
 #include <linux/memremap.h>
 #include <linux/mm.h>
+#include <linux/vmemmap-optimization.h>
 #include <linux/mman.h>
 #include <linux/highmem.h>
 #include <linux/swap.h>
@@ -143,6 +144,7 @@ void __meminit vmemmap_set_pmd(pmd_t *pm
 int __meminit vmemmap_populate(unsigned long start, unsigned long end,
 			       int node, struct vmem_altmap *altmap)
 {
+	section_vmemmap_optimization_disable(start, end);
 #if CONFIG_PGTABLE_LEVELS == 2
 	return vmemmap_populate_basepages(start, end, node, NULL);
 #else
_

Patches currently in -mm which might be from muchun.song@linux.dev are

mm-fix-missing-page-table-destructor-in-pagetable_free.patch
riscv-mm-fix-hotplug-page-table-destructor-handling.patch
riscv-mm-fix-missing-destructor-for-hotplug-pud-tables.patch
arm64-mm-fix-destructor-for-unconstructed-hotplug-page-tables.patch
mm-sparse-vmemmap-map-shared-vmemmap-tail-pages-as-read-only.patch
powerpc-mm-map-shared-vmemmap-tail-pages-as-read-only.patch
mm-hugetlb_vmemmap-remove-vmemmap_wrprotect_hvo.patch
mm-hugetlb_vmemmap-remove-hugetlb_vmemmap_optimize_bootmem_folios.patch
mm-generalize-kernel-pte-table-allocation.patch
mm-generalize-pmd-page-table-allocation.patch
mm-generalize-pud-page-table-allocation.patch
mm-remove-pagetable_dtor_free.patch
mm-remove-redundant-pagetable_dtor-calls.patch
mm-hugetlb_vmemmap-remove-hugetlb-specific-vmemmap-optimization-macros.patch
mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.patch
mm-hugetlb_vmemmap-simplify-vmemmap-head-page-handling.patch
mm-hugetlb_vmemmap-generalize-vmemmap-page-allocation.patch
mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch
mm-hugetlb_vmemmap-rename-vmemmap_remap_pte-to-vmemmap_optimize_pte.patch
mm-hugetlb_vmemmap-simplify-shared-tail-page-handling.patch
mm-hugetlb_vmemmap-move-alloc_vmemmap_page_list-next-to-its-free-helper.patch
mm-hugetlb_vmemmap-make-vmemmap-optimization-folio-oriented.patch
mm-hugetlb_vmemmap-make-vmemmap-restoration-folio-oriented.patch
mm-hugetlb_vmemmap-unify-vmemmap-range-restoration.patch
mm-hugetlb_vmemmap-make-vmemmap-pte-conversion-folio-oriented.patch
mm-hugetlb-fix-validation-of-unsupported-hugetlb-orders.patch
powerpc-mm-make-vmemmap_populate_compound_pages-static.patch
powerpc-mm-drop-powerpc-vmemmap_can_optimize.patch
loongarch-mm-disable-device-dax-vmemmap-optimization.patch
mm-sparse-vmemmap-drop-vmemmap_can_optimize.patch
mm-sparse-vmemmap-drop-pgmap-from-vmemmap-population-apis.patch