[RFC PATCH v2 09/30] mm: thp: add PUD THP support to zap_huge_pud.

[Zi Yan <zi.yan@xxxxxxxx>]

From: Zi Yan <ziy@xxxxxxxxxx>

Preallocated 513 (1 PMD and 512 PTE) page table pages need to be freed
when PUD THP is removed. zap_pud_deposited_table is added to perform the
action.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 mm/huge_memory.c | 48 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ea9fbedcda26..76069affebef 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2013,11 +2013,27 @@ spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+static inline void zap_pud_deposited_table(struct mm_struct *mm, pud_t *pud)
+{
+	pgtable_t pgtable;
+	int i;
+
+	pgtable = pgtable_trans_huge_pud_withdraw(mm, pud);
+	pmd_free_page_with_ptes(mm, (pmd_t *)page_address(pgtable));
+
+	mm_dec_nr_pmds(mm);
+	for (i = 0; i < (1<<(HPAGE_PUD_ORDER - HPAGE_PMD_ORDER)); i++)
+		mm_dec_nr_ptes(mm);
+}
+
 int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		 pud_t *pud, unsigned long addr)
 {
+	pud_t orig_pud;
 	spinlock_t *ptl;
 
+	tlb_change_page_size(tlb, HPAGE_PUD_SIZE);
+
 	ptl = __pud_trans_huge_lock(pud, vma);
 	if (!ptl)
 		return 0;
@@ -2027,14 +2043,40 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	 * pgtable_trans_huge_withdraw after finishing pudp related
 	 * operations.
 	 */
-	pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
+	orig_pud = pudp_huge_get_and_clear_full(tlb->mm, addr, pud,
+			tlb->fullmm);
 	tlb_remove_pud_tlb_entry(tlb, pud, addr);
 	if (vma_is_special_huge(vma)) {
 		spin_unlock(ptl);
 		/* No zero page support yet */
+	} else if (is_huge_zero_pud(orig_pud)) {
+		zap_pud_deposited_table(tlb->mm, pud);
+		spin_unlock(ptl);
+		tlb_remove_page_size(tlb, pud_page(orig_pud), HPAGE_PUD_SIZE);
 	} else {
-		/* No support for anonymous PUD pages yet */
-		BUG();
+		struct page *page = NULL;
+		int flush_needed = 1;
+
+		if (pud_present(orig_pud)) {
+			page = pud_page(orig_pud);
+			page_remove_rmap(page, true);
+			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
+			VM_BUG_ON_PAGE(!PageHead(page), page);
+		} else
+			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+
+		if (PageAnon(page)) {
+			zap_pud_deposited_table(tlb->mm, pud);
+			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PUD_NR);
+		} else {
+			if (arch_needs_pgtable_deposit())
+				zap_pud_deposited_table(tlb->mm, pud);
+			add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PUD_NR);
+		}
+
+		spin_unlock(ptl);
+		if (flush_needed)
+			tlb_remove_page_size(tlb, page, HPAGE_PUD_SIZE);
 	}
 	return 1;
 }
-- 
2.28.0