[PATCH 06/12] huge_memory: Allow mappings of PUD sized pages

From: Alistair Popple
Date: Tue Sep 10 2024 - 00:18:06 EST

Currently DAX folio/page reference counts are managed differently to
normal pages. To allow these to be managed the same as normal pages
introduce dax_insert_pfn_pud. This will map the entire PUD-sized folio
and take references as it would for a normally mapped page.

This is distinct from the current mechanism, vmf_insert_pfn_pud, which
simply inserts a special devmap PUD entry into the page table without
holding a reference to the page for the mapping.

Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
---
include/linux/huge_mm.h | 4 ++-
include/linux/rmap.h | 15 +++++++-
mm/huge_memory.c | 93 ++++++++++++++++++++++++++++++++++++------
mm/rmap.c | 49 ++++++++++++++++++++++-
4 files changed, 149 insertions(+), 12 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 6370026..d3a1872 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -40,6 +40,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,

vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
+vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);

enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_UNSUPPORTED,
@@ -114,6 +115,9 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
#define HPAGE_PUD_MASK (~(HPAGE_PUD_SIZE - 1))
#define HPAGE_PUD_SIZE ((1UL) << HPAGE_PUD_SHIFT)

+#define HPAGE_PUD_ORDER (HPAGE_PUD_SHIFT-PAGE_SHIFT)
+#define HPAGE_PUD_NR (1<<HPAGE_PUD_ORDER)
+
#ifdef CONFIG_TRANSPARENT_HUGEPAGE

extern unsigned long transparent_hugepage_flags;
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 91b5935..c465694 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -192,6 +192,7 @@ typedef int __bitwise rmap_t;
enum rmap_level {
RMAP_LEVEL_PTE = 0,
RMAP_LEVEL_PMD,
+ RMAP_LEVEL_PUD,
};

static inline void __folio_rmap_sanity_checks(struct folio *folio,
@@ -228,6 +229,14 @@ static inline void __folio_rmap_sanity_checks(struct folio *folio,
VM_WARN_ON_FOLIO(folio_nr_pages(folio) != HPAGE_PMD_NR, folio);
VM_WARN_ON_FOLIO(nr_pages != HPAGE_PMD_NR, folio);
break;
+ case RMAP_LEVEL_PUD:
+ /*
+ * Asume that we are creating * a single "entire" mapping of the
+ * folio.
+ */
+ VM_WARN_ON_FOLIO(folio_nr_pages(folio) != HPAGE_PUD_NR, folio);
+ VM_WARN_ON_FOLIO(nr_pages != HPAGE_PUD_NR, folio);
+ break;
default:
VM_WARN_ON_ONCE(true);
}
@@ -251,12 +260,16 @@ void folio_add_file_rmap_ptes(struct folio *, struct page *, int nr_pages,
folio_add_file_rmap_ptes(folio, page, 1, vma)
void folio_add_file_rmap_pmd(struct folio *, struct page *,
struct vm_area_struct *);
+void folio_add_file_rmap_pud(struct folio *, struct page *,
+ struct vm_area_struct *);
void folio_remove_rmap_ptes(struct folio *, struct page *, int nr_pages,
struct vm_area_struct *);
#define folio_remove_rmap_pte(folio, page, vma) \
folio_remove_rmap_ptes(folio, page, 1, vma)
void folio_remove_rmap_pmd(struct folio *, struct page *,
struct vm_area_struct *);
+void folio_remove_rmap_pud(struct folio *, struct page *,
+ struct vm_area_struct *);

void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
unsigned long address, rmap_t flags);
@@ -341,6 +354,7 @@ static __always_inline void __folio_dup_file_rmap(struct folio *folio,
atomic_add(orig_nr_pages, &folio->_large_mapcount);
break;
case RMAP_LEVEL_PMD:
+ case RMAP_LEVEL_PUD:
atomic_inc(&folio->_entire_mapcount);
atomic_inc(&folio->_large_mapcount);
break;
@@ -437,6 +451,7 @@ static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio,
atomic_add(orig_nr_pages, &folio->_large_mapcount);
break;
case RMAP_LEVEL_PMD:
+ case RMAP_LEVEL_PUD:
if (PageAnonExclusive(page)) {
if (unlikely(maybe_pinned))
return -EBUSY;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c4b45ad..e8985a4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1336,21 +1336,19 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
struct mm_struct *mm = vma->vm_mm;
pgprot_t prot = vma->vm_page_prot;
pud_t entry;
- spinlock_t *ptl;

- ptl = pud_lock(mm, pud);
if (!pud_none(*pud)) {
if (write) {
if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
WARN_ON_ONCE(!is_huge_zero_pud(*pud));
- goto out_unlock;
+ return;
}
entry = pud_mkyoung(*pud);
entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
if (pudp_set_access_flags(vma, addr, pud, entry, 1))
update_mmu_cache_pud(vma, addr, pud);
}
- goto out_unlock;
+ return;
}

entry = pud_mkhuge(pfn_t_pud(pfn, prot));
@@ -1362,9 +1360,6 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
}
set_pud_at(mm, addr, pud, entry);
update_mmu_cache_pud(vma, addr, pud);
-
-out_unlock:
- spin_unlock(ptl);
}

/**
@@ -1382,6 +1377,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
unsigned long addr = vmf->address & PUD_MASK;
struct vm_area_struct *vma = vmf->vma;
pgprot_t pgprot = vma->vm_page_prot;
+ spinlock_t *ptl;

/*
* If we had pud_special, we could avoid all these restrictions,
@@ -1399,10 +1395,52 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)

track_pfn_insert(vma, &pgprot, pfn);

+ ptl = pud_lock(vma->vm_mm, vmf->pud);
insert_pfn_pud(vma, addr, vmf->pud, pfn, write);
+ spin_unlock(ptl);
+
return VM_FAULT_NOPAGE;
}
EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud);
+
+/**
+ * dax_insert_pfn_pud - insert a pud size pfn backed by a normal page
+ * @vmf: Structure describing the fault
+ * @pfn: pfn of the page to insert
+ * @write: whether it's a write fault
+ *
+ * Return: vm_fault_t value.
+ */
+vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned long addr = vmf->address & PUD_MASK;
+ pud_t *pud = vmf->pud;
+ pgprot_t prot = vma->vm_page_prot;
+ struct mm_struct *mm = vma->vm_mm;
+ spinlock_t *ptl;
+ struct folio *folio;
+ struct page *page;
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return VM_FAULT_SIGBUS;
+
+ track_pfn_insert(vma, &prot, pfn);
+
+ ptl = pud_lock(mm, pud);
+ if (pud_none(*vmf->pud)) {
+ page = pfn_t_to_page(pfn);
+ folio = page_folio(page);
+ folio_get(folio);
+ folio_add_file_rmap_pud(folio, page, vma);
+ add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR);
+ }
+ insert_pfn_pud(vma, addr, vmf->pud, pfn, write);
+ spin_unlock(ptl);
+
+ return VM_FAULT_NOPAGE;
+}
+EXPORT_SYMBOL_GPL(dax_insert_pfn_pud);
#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */

void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
@@ -1947,7 +1985,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
zap_deposited_table(tlb->mm, pmd);
spin_unlock(ptl);
} else if (is_huge_zero_pmd(orig_pmd)) {
- zap_deposited_table(tlb->mm, pmd);
+ if (!vma_is_dax(vma) || arch_needs_pgtable_deposit())
+ zap_deposited_table(tlb->mm, pmd);
spin_unlock(ptl);
} else {
struct folio *folio = NULL;
@@ -2435,12 +2474,24 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
orig_pud = pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fullmm);
arch_check_zapped_pud(vma, orig_pud);
tlb_remove_pud_tlb_entry(tlb, pud, addr);
- if (vma_is_special_huge(vma)) {
+ if (!vma_is_dax(vma) && vma_is_special_huge(vma)) {
spin_unlock(ptl);
/* No zero page support yet */
} else {
- /* No support for anonymous PUD pages yet */
- BUG();
+ struct page *page = NULL;
+ struct folio *folio;
+
+ /* No support for anonymous PUD pages or migration yet */
+ BUG_ON(vma_is_anonymous(vma) || !pud_present(orig_pud));
+
+ page = pud_page(orig_pud);
+ folio = page_folio(page);
+ folio_remove_rmap_pud(folio, page, vma);
+ VM_BUG_ON_PAGE(!PageHead(page), page);
+ add_mm_counter(tlb->mm, mm_counter_file(folio), -HPAGE_PUD_NR);
+
+ spin_unlock(ptl);
+ tlb_remove_page_size(tlb, page, HPAGE_PUD_SIZE);
}
return 1;
}
@@ -2448,6 +2499,8 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
unsigned long haddr)
{
+ pud_t old_pud;
+
VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
@@ -2455,7 +2508,23 @@ static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,

count_vm_event(THP_SPLIT_PUD);

- pudp_huge_clear_flush(vma, haddr, pud);
+ old_pud = pudp_huge_clear_flush(vma, haddr, pud);
+ if (is_huge_zero_pud(old_pud))
+ return;
+
+ if (vma_is_dax(vma)) {
+ struct page *page = pud_page(old_pud);
+ struct folio *folio = page_folio(page);
+
+ if (!folio_test_dirty(folio) && pud_dirty(old_pud))
+ folio_mark_dirty(folio);
+ if (!folio_test_referenced(folio) && pud_young(old_pud))
+ folio_set_referenced(folio);
+ folio_remove_rmap_pud(folio, page, vma);
+ folio_put(folio);
+ add_mm_counter(vma->vm_mm, mm_counter_file(folio),
+ -HPAGE_PUD_NR);
+ }
}

void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
diff --git a/mm/rmap.c b/mm/rmap.c
index 1103a53..274641c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1180,6 +1180,7 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio,
atomic_add(orig_nr_pages, &folio->_large_mapcount);
break;
case RMAP_LEVEL_PMD:
+ case RMAP_LEVEL_PUD:
first = atomic_inc_and_test(&folio->_entire_mapcount);
if (first) {
nr = atomic_add_return_relaxed(ENTIRELY_MAPPED, mapped);
@@ -1330,6 +1331,13 @@ static __always_inline void __folio_add_anon_rmap(struct folio *folio,
case RMAP_LEVEL_PMD:
SetPageAnonExclusive(page);
break;
+ case RMAP_LEVEL_PUD:
+ /*
+ * Keep the compiler happy, we don't support anonymous
+ * PUD mappings.
+ */
+ WARN_ON_ONCE(1);
+ break;
}
}
for (i = 0; i < nr_pages; i++) {
@@ -1522,6 +1530,26 @@ void folio_add_file_rmap_pmd(struct folio *folio, struct page *page,
#endif
}

+/**
+ * folio_add_file_rmap_pud - add a PUD mapping to a page range of a folio
+ * @folio: The folio to add the mapping to
+ * @page: The first page to add
+ * @vma: The vm area in which the mapping is added
+ *
+ * The page range of the folio is defined by [page, page + HPAGE_PUD_NR)
+ *
+ * The caller needs to hold the page table lock.
+ */
+void folio_add_file_rmap_pud(struct folio *folio, struct page *page,
+ struct vm_area_struct *vma)
+{
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+ __folio_add_file_rmap(folio, page, HPAGE_PUD_NR, vma, RMAP_LEVEL_PUD);
+#else
+ WARN_ON_ONCE(true);
+#endif
+}
+
static __always_inline void __folio_remove_rmap(struct folio *folio,
struct page *page, int nr_pages, struct vm_area_struct *vma,
enum rmap_level level)
@@ -1551,6 +1579,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
partially_mapped = nr && atomic_read(mapped);
break;
case RMAP_LEVEL_PMD:
+ case RMAP_LEVEL_PUD:
atomic_dec(&folio->_large_mapcount);
last = atomic_add_negative(-1, &folio->_entire_mapcount);
if (last) {
@@ -1630,6 +1659,26 @@ void folio_remove_rmap_pmd(struct folio *folio, struct page *page,
#endif
}

+/**
+ * folio_remove_rmap_pud - remove a PUD mapping from a page range of a folio
+ * @folio: The folio to remove the mapping from
+ * @page: The first page to remove
+ * @vma: The vm area from which the mapping is removed
+ *
+ * The page range of the folio is defined by [page, page + HPAGE_PUD_NR)
+ *
+ * The caller needs to hold the page table lock.
+ */
+void folio_remove_rmap_pud(struct folio *folio, struct page *page,
+ struct vm_area_struct *vma)
+{
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+ __folio_remove_rmap(folio, page, HPAGE_PUD_NR, vma, RMAP_LEVEL_PUD);
+#else
+ WARN_ON_ONCE(true);
+#endif
+}
+
/*
* @arg: enum ttu_flags will be passed to this argument
*/
--
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