[RFC PATCH v2 08/30] mm: thp: add PUD THP support for copy_huge_pud.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

copy_huge_pud needs to allocate 1 PMD page table page and 512 PTE page
table pages and deposit them when copying a PUD THP. It is similar to
what we do at PUD THP page faults.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 mm/huge_memory.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 20a3d393d451..ea9fbedcda26 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1264,7 +1264,12 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 {
 	spinlock_t *dst_ptl, *src_ptl;
 	pud_t pud;
-	int ret;
+	pmd_t *pmd_pgtable = NULL;
+	int ret = -ENOMEM;
+
+	pmd_pgtable = pmd_alloc_one_page_with_ptes(vma->vm_mm, addr);
+	if (unlikely(!pmd_pgtable))
+		goto out;
 
 	dst_ptl = pud_lock(dst_mm, dst_pud);
 	src_ptl = pud_lockptr(src_mm, src_pud);
@@ -1272,16 +1277,30 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
 	ret = -EAGAIN;
 	pud = *src_pud;
-	if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
-		goto out_unlock;
 
 	/*
-	 * When page table lock is held, the huge zero pud should not be
-	 * under splitting since we don't split the page itself, only pud to
-	 * a page table.
+	 * only transparent huge pud page needs extra page table pages for
+	 * possible huge page split
 	 */
-	if (is_huge_zero_pud(pud)) {
-		/* No huge zero pud yet */
+	if (!pud_trans_huge(pud))
+		pmd_free_page_with_ptes(dst_mm, pmd_pgtable);
+
+	if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
+		goto out_unlock;
+
+	if (pud_trans_huge(pud)) {
+		struct page *src_page;
+		int i;
+
+		src_page = pud_page(pud);
+		VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
+		get_page(src_page);
+		page_dup_rmap(src_page, true);
+		add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PUD_NR);
+		mm_inc_nr_pmds(dst_mm);
+		for (i = 0; i < (1<<(HPAGE_PUD_ORDER - HPAGE_PMD_ORDER)); i++)
+			mm_inc_nr_ptes(dst_mm);
+		pgtable_trans_huge_pud_deposit(dst_mm, dst_pud, virt_to_page(pmd_pgtable));
 	}
 
 	pudp_set_wrprotect(src_mm, addr, src_pud);
@@ -1292,6 +1311,7 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 out_unlock:
 	spin_unlock(src_ptl);
 	spin_unlock(dst_ptl);
+out:
 	return ret;
 }
 
-- 
2.28.0