[PATCHv6 08/30] thp: support file pages in zap_huge_pmd()

[Kirill A. Shutemov]

split_huge_pmd() for file mappings (and DAX too) is implemented by just
clearing pmd entry as we can re-fill this area from page cache on pte
level later.

This means we don't need deposit page tables when file THP is mapped.
Therefore we shouldn't try to withdraw a page table on zap_huge_pmd()
file THP PMD.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/huge_memory.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8c76f12ea097..5975c14d66ab 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1696,10 +1696,16 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		struct page *page = pmd_page(orig_pmd);
 		page_remove_rmap(page, true);
 		VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
-		add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
 		VM_BUG_ON_PAGE(!PageHead(page), page);
-		pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
-		atomic_long_dec(&tlb->mm->nr_ptes);
+		if (PageAnon(page)) {
+			pgtable_t pgtable;
+			pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
+			pte_free(tlb->mm, pgtable);
+			atomic_long_dec(&tlb->mm->nr_ptes);
+			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+		} else {
+			add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
+		}
 		spin_unlock(ptl);
 		tlb_remove_page(tlb, page);
 	}
-- 
2.8.0.rc3