[PATCH 1/7] mm: Document x86 uses a linked list of pgds

[Matthew Wilcox]

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

x86 uses page->lru of the pages used for pgds, but that's not immediately
obvious to anyone looking to make changes.  Add a struct list_head to
the union so it's clearly in use for pgds.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 include/linux/mm_types.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4aba6c0c2ba8..9bb34e2cd5a5 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -142,8 +142,13 @@ struct page {
 			struct list_head deferred_list;
 		};
 		struct {	/* Page table pages */
-			unsigned long _pt_pad_1;	/* compound_head */
-			pgtable_t pmd_huge_pte; /* protected by page->ptl */
+			union {
+				struct list_head pgd_list;	/* x86 */
+				struct {
+					unsigned long _pt_pad_1;
+					pgtable_t pmd_huge_pte;
+				};
+			};
 			unsigned long _pt_pad_2;	/* mapping */
 			union {
 				struct mm_struct *pt_mm; /* x86 pgds only */
-- 
2.26.2