[PATCH 2/7] mm: Move pt_mm within struct page

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

Instead of a per-arch word within struct page, use a formerly reserved
word.  This word is shared with page->mapping, so it must be cleared
before being freed as it is checked in free_pages().

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 arch/x86/mm/pgtable.c    | 1 +
 include/linux/mm_types.h | 7 ++-----
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 7bd2c3a52297..f5f46737aea0 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -95,6 +95,7 @@ static inline void pgd_list_del(pgd_t *pgd)
 	struct page *page = virt_to_page(pgd);
 
 	list_del(&page->lru);
+	page->pt_mm = NULL;
 }
 
 #define UNSHARED_PTRS_PER_PGD				\
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9bb34e2cd5a5..7efa12f4626f 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -149,11 +149,8 @@ struct page {
 					pgtable_t pmd_huge_pte;
 				};
 			};
-			unsigned long _pt_pad_2;	/* mapping */
-			union {
-				struct mm_struct *pt_mm; /* x86 pgds only */
-				atomic_t pt_frag_refcount; /* powerpc */
-			};
+			struct mm_struct *pt_mm;
+			atomic_t pt_frag_refcount; /* powerpc */
 #if ALLOC_SPLIT_PTLOCKS
 			spinlock_t *ptl;
 #else
-- 
2.26.2