[RFC PATCH 04/16] mm: thp: 1GB THP copy on write implementation.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

COW on 1GB THPs will fall back to 2MB THPs if 1GB THP is not available.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 arch/x86/include/asm/pgalloc.h |  9 ++++++
 include/linux/huge_mm.h        |  5 ++++
 mm/huge_memory.c               | 54 ++++++++++++++++++++++++++++++++++
 mm/memory.c                    |  2 +-
 mm/swapfile.c                  |  4 ++-
 5 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index fae13467d3e1..31221269c387 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -98,6 +98,15 @@ static inline void pmd_populate(struct mm_struct *mm, pmd_t *pmd,
 
 #define pmd_pgtable(pmd) pmd_page(pmd)
 
+static inline void pud_populate_with_pgtable(struct mm_struct *mm, pud_t *pud,
+				struct page *pte)
+{
+	unsigned long pfn = page_to_pfn(pte);
+
+	paravirt_alloc_pmd(mm, pfn);
+	set_pud(pud, __pud(((pteval_t)pfn << PAGE_SHIFT) | _PAGE_TABLE));
+}
+
 #if CONFIG_PGTABLE_LEVELS > 2
 static inline pmd_t *pmd_alloc_one_page_with_ptes(struct mm_struct *mm, unsigned long addr)
 {
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 7528652400e4..0c20a8ea6911 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -19,6 +19,7 @@ extern int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 extern void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud);
 extern int do_huge_pud_anonymous_page(struct vm_fault *vmf);
+extern vm_fault_t do_huge_pud_wp_page(struct vm_fault *vmf, pud_t orig_pud);
 #else
 static inline void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
 {
@@ -27,6 +28,10 @@ extern int do_huge_pud_anonymous_page(struct vm_fault *vmf)
 {
 	return VM_FAULT_FALLBACK;
 }
+extern vm_fault_t do_huge_pud_wp_page(struct vm_fault *vmf, pud_t orig_pud)
+{
+	return VM_FAULT_FALLBACK;
+}
 #endif
 
 extern vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ec3847392208..6da9b02501b7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1334,6 +1334,60 @@ void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
 unlock:
 	spin_unlock(vmf->ptl);
 }
+
+vm_fault_t do_huge_pud_wp_page(struct vm_fault *vmf, pud_t orig_pud)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page = NULL;
+	unsigned long haddr = vmf->address & HPAGE_PUD_MASK;
+
+	vmf->ptl = pud_lockptr(vma->vm_mm, vmf->pud);
+	VM_BUG_ON_VMA(!vma->anon_vma, vma);
+
+	if (is_huge_zero_pud(orig_pud))
+		goto fallback;
+
+	spin_lock(vmf->ptl);
+
+	if (unlikely(!pud_same(*vmf->pud, orig_pud))) {
+		spin_unlock(vmf->ptl);
+		return 0;
+	}
+
+	page = pud_page(orig_pud);
+	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
+
+	/* Lock page for reuse_swap_page() */
+	if (!trylock_page(page)) {
+		get_page(page);
+		spin_unlock(vmf->ptl);
+		lock_page(page);
+		spin_lock(vmf->ptl);
+		if (unlikely(!pud_same(*vmf->pud, orig_pud))) {
+			unlock_page(page);
+			put_page(page);
+			return 0;
+		}
+		put_page(page);
+	}
+	if (reuse_swap_page(page, NULL)) {
+		pud_t entry;
+
+		entry = pud_mkyoung(orig_pud);
+		entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
+		if (pudp_set_access_flags(vma, haddr, vmf->pud, entry,  1))
+			update_mmu_cache_pud(vma, vmf->address, vmf->pud);
+		unlock_page(page);
+		spin_unlock(vmf->ptl);
+		return VM_FAULT_WRITE;
+	}
+	unlock_page(page);
+	spin_unlock(vmf->ptl);
+fallback:
+	__split_huge_pud(vma, vmf->pud, vmf->address);
+	return VM_FAULT_FALLBACK;
+}
+
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
 void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
diff --git a/mm/memory.c b/mm/memory.c
index 6f86294438fd..b88587256bc1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4165,7 +4165,7 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	/* No support for anonymous transparent PUD pages yet */
 	if (vma_is_anonymous(vmf->vma))
-		return VM_FAULT_FALLBACK;
+		return do_huge_pud_wp_page(vmf, orig_pud);
 	if (vmf->vma->vm_ops->huge_fault)
 		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 20012c0c0252..e3f771c2ad83 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1635,7 +1635,9 @@ static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
 	/* hugetlbfs shouldn't call it */
 	VM_BUG_ON_PAGE(PageHuge(page), page);
 
-	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
+	if (!IS_ENABLED(CONFIG_THP_SWAP) ||
+	    unlikely(compound_order(compound_head(page)) == HPAGE_PUD_ORDER) ||
+	    likely(!PageTransCompound(page))) {
 		mapcount = page_trans_huge_mapcount(page, total_mapcount);
 		if (PageSwapCache(page))
 			swapcount = page_swapcount(page);
-- 
2.28.0