Add support for splitting device-private THP folios, enabling fallback
to smaller page sizes when large page allocation or migration fails.
Key changes:
- split_huge_pmd(): Handle device-private PMD entries during splitting
- Preserve RMAP_EXCLUSIVE semantics for anonymous exclusive folios
- Skip RMP_USE_SHARED_ZEROPAGE for device-private entries as they
don't support shared zero page semantics
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
---
mm/huge_memory.c | 87 +++++++++++++++++++++++++++++++++++++++++-------
mm/migrate.c | 1 +
2 files changed, 76 insertions(+), 12 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 483b8341ce22..05c68f5b5fe3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2872,16 +2872,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
struct page *page;
pgtable_t pgtable;
pmd_t old_pmd, _pmd;
- bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
+ bool soft_dirty, uffd_wp = false, young = false, write = false;
bool anon_exclusive = false, dirty = false;
unsigned long addr;
pte_t *pte;
int i;
+ swp_entry_t entry;
VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
- VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd));
+
+ VM_WARN_ON(!is_pmd_non_present_folio_entry(*pmd) && !pmd_trans_huge(*pmd));
count_vm_event(THP_SPLIT_PMD);
@@ -2929,20 +2931,51 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
return __split_huge_zero_page_pmd(vma, haddr, pmd);
}
- pmd_migration = is_pmd_migration_entry(*pmd);
- if (unlikely(pmd_migration)) {
- swp_entry_t entry;
+ if (is_pmd_migration_entry(*pmd)) {
old_pmd = *pmd;
entry = pmd_to_swp_entry(old_pmd);
page = pfn_swap_entry_to_page(entry);
+ folio = page_folio(page);
+
+ soft_dirty = pmd_swp_soft_dirty(old_pmd);
+ uffd_wp = pmd_swp_uffd_wp(old_pmd);
+
write = is_writable_migration_entry(entry);
if (PageAnon(page))
anon_exclusive = is_readable_exclusive_migration_entry(entry);
young = is_migration_entry_young(entry);
dirty = is_migration_entry_dirty(entry);
+ } else if (is_pmd_device_private_entry(*pmd)) {
+ old_pmd = *pmd;
+ entry = pmd_to_swp_entry(old_pmd);
+ page = pfn_swap_entry_to_page(entry);
+ folio = page_folio(page);
+
soft_dirty = pmd_swp_soft_dirty(old_pmd);
uffd_wp = pmd_swp_uffd_wp(old_pmd);
+
+ write = is_writable_device_private_entry(entry);
+ anon_exclusive = PageAnonExclusive(page);
+
+ /*
+ * Device private THP should be treated the same as regular
+ * folios w.r.t anon exclusive handling. See the comments for
+ * folio handling and anon_exclusive below.
+ */
+ if (freeze && anon_exclusive &&
+ folio_try_share_anon_rmap_pmd(folio, page))
+ freeze = false;
+ if (!freeze) {
+ rmap_t rmap_flags = RMAP_NONE;
+
+ folio_ref_add(folio, HPAGE_PMD_NR - 1);
+ if (anon_exclusive)
+ rmap_flags |= RMAP_EXCLUSIVE;
+
+ folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR,
+ vma, haddr, rmap_flags);
+ }
} else {
/*
* Up to this point the pmd is present and huge and userland has
@@ -3026,11 +3059,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
* Note that NUMA hinting access restrictions are not transferred to
* avoid any possibility of altering permissions across VMAs.
*/
- if (freeze || pmd_migration) {
- for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
- pte_t entry;
- swp_entry_t swp_entry;
+ if (freeze || is_pmd_migration_entry(old_pmd)) {
+ pte_t entry;
+ swp_entry_t swp_entry;
+ for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
if (write)
swp_entry = make_writable_migration_entry(
page_to_pfn(page + i));
@@ -3049,7 +3082,33 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
entry = pte_swp_mksoft_dirty(entry);
if (uffd_wp)
entry = pte_swp_mkuffd_wp(entry);
+ VM_WARN_ON(!pte_none(ptep_get(pte + i)));
+ set_pte_at(mm, addr, pte + i, entry);
+ }
+ } else if (is_pmd_device_private_entry(old_pmd)) {
+ pte_t entry;
+ swp_entry_t swp_entry;
+ for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
+ /*
+ * anon_exclusive was already propagated to the relevant
+ * pages corresponding to the pte entries when freeze
+ * is false.
+ */
+ if (write)
+ swp_entry = make_writable_device_private_entry(
+ page_to_pfn(page + i));
+ else
+ swp_entry = make_readable_device_private_entry(
+ page_to_pfn(page + i));
+ /*
+ * Young and dirty bits are not progated via swp_entry
+ */
+ entry = swp_entry_to_pte(swp_entry);
+ if (soft_dirty)
+ entry = pte_swp_mksoft_dirty(entry);
+ if (uffd_wp)
+ entry = pte_swp_mkuffd_wp(entry);
VM_WARN_ON(!pte_none(ptep_get(pte + i)));
set_pte_at(mm, addr, pte + i, entry);
}
@@ -3076,7 +3135,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
}
pte_unmap(pte);
- if (!pmd_migration)
+ if (!is_pmd_migration_entry(*pmd))
folio_remove_rmap_pmd(folio, page, vma);
if (freeze)
put_page(page);
@@ -3089,7 +3148,7 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmd, bool freeze)
{
VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE));
- if (pmd_trans_huge(*pmd) || is_pmd_migration_entry(*pmd))
+ if (pmd_trans_huge(*pmd) || is_pmd_non_present_folio_entry(*pmd))
__split_huge_pmd_locked(vma, pmd, address, freeze);
}
@@ -3268,6 +3327,9 @@ static void lru_add_split_folio(struct folio *folio, struct folio *new_folio,
VM_BUG_ON_FOLIO(folio_test_lru(new_folio), folio);
lockdep_assert_held(&lruvec->lru_lock);
+ if (folio_is_device_private(folio))
+ return;
+
if (list) {
/* page reclaim is reclaiming a huge page */
VM_WARN_ON(folio_test_lru(folio));
@@ -3885,8 +3947,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
if (nr_shmem_dropped)
shmem_uncharge(mapping->host, nr_shmem_dropped);
- if (!ret && is_anon)
+ if (!ret && is_anon && !folio_is_device_private(folio))
remap_flags = RMP_USE_SHARED_ZEROPAGE;
+
remap_page(folio, 1 << order, remap_flags);
/*
diff --git a/mm/migrate.c b/mm/migrate.c
index ce83c2c3c287..11fbfe905e3c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -307,6 +307,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
VM_BUG_ON_PAGE(!PageAnon(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
+ VM_WARN_ON_ONCE_FOLIO(folio_is_device_private(folio), folio);
if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) ||
mm_forbids_zeropage(pvmw->vma->vm_mm))
--
2.51.0