[PATCH v3 09/16] mm/huge_memory: refactor change_huge_pmd() non-present logic

Lorenzo Stoakes
2025-11-10T22:24:04Z

Similar to copy_huge_pmd(), there is a large mass of open-coded logic for
the CONFIG_ARCH_ENABLE_THP_MIGRATION non-present entry case that does not
use thp_migration_supported() consistently.

Resolve this by separating out this logic and introduce
change_non_present_huge_pmd().

No functional change intended.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
mm/huge_memory.c | 72 ++++++++++++++++++++++++++----------------------
1 file changed, 39 insertions(+), 33 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 31116d69e289..40a8a2c1e080 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2499,6 +2499,42 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
return false;
}

+static void change_non_present_huge_pmd(struct mm_struct *mm,
+ unsigned long addr, pmd_t *pmd, bool uffd_wp,
+ bool uffd_wp_resolve)
+{
+ swp_entry_t entry = pmd_to_swp_entry(*pmd);
+ struct folio *folio = pfn_swap_entry_folio(entry);
+ pmd_t newpmd;
+
+ VM_WARN_ON(!is_pmd_non_present_folio_entry(*pmd));
+ if (is_writable_migration_entry(entry)) {
+ /*
+ * A protection check is difficult so
+ * just be safe and disable write
+ */
+ if (folio_test_anon(folio))
+ entry = make_readable_exclusive_migration_entry(swp_offset(entry));
+ else
+ entry = make_readable_migration_entry(swp_offset(entry));
+ newpmd = swp_entry_to_pmd(entry);
+ if (pmd_swp_soft_dirty(*pmd))
+ newpmd = pmd_swp_mksoft_dirty(newpmd);
+ } else if (is_writable_device_private_entry(entry)) {
+ entry = make_readable_device_private_entry(swp_offset(entry));
+ newpmd = swp_entry_to_pmd(entry);
+ } else {
+ newpmd = *pmd;
+ }
+
+ if (uffd_wp)
+ newpmd = pmd_swp_mkuffd_wp(newpmd);
+ else if (uffd_wp_resolve)
+ newpmd = pmd_swp_clear_uffd_wp(newpmd);
+ if (!pmd_same(*pmd, newpmd))
+ set_pmd_at(mm, addr, pmd, newpmd);
+}
+
/*
* Returns
* - 0 if PMD could not be locked
@@ -2527,41 +2563,11 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
if (!ptl)
return 0;

-#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
- if (is_swap_pmd(*pmd)) {
- swp_entry_t entry = pmd_to_swp_entry(*pmd);
- struct folio *folio = pfn_swap_entry_folio(entry);
- pmd_t newpmd;
-
- VM_WARN_ON(!is_pmd_non_present_folio_entry(*pmd));
- if (is_writable_migration_entry(entry)) {
- /*
- * A protection check is difficult so
- * just be safe and disable write
- */
- if (folio_test_anon(folio))
- entry = make_readable_exclusive_migration_entry(swp_offset(entry));
- else
- entry = make_readable_migration_entry(swp_offset(entry));
- newpmd = swp_entry_to_pmd(entry);
- if (pmd_swp_soft_dirty(*pmd))
- newpmd = pmd_swp_mksoft_dirty(newpmd);
- } else if (is_writable_device_private_entry(entry)) {
- entry = make_readable_device_private_entry(swp_offset(entry));
- newpmd = swp_entry_to_pmd(entry);
- } else {
- newpmd = *pmd;
- }
-
- if (uffd_wp)
- newpmd = pmd_swp_mkuffd_wp(newpmd);
- else if (uffd_wp_resolve)
- newpmd = pmd_swp_clear_uffd_wp(newpmd);
- if (!pmd_same(*pmd, newpmd))
- set_pmd_at(mm, addr, pmd, newpmd);
+ if (thp_migration_supported() && is_swap_pmd(*pmd)) {
+ change_non_present_huge_pmd(mm, addr, pmd, uffd_wp,
+ uffd_wp_resolve);
goto unlock;
}
-#endif

if (prot_numa) {

--
2.51.0