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

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Date:   Tue, 28 Apr 2020 12:44:43 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Subject: [PATCH 1/7] mm: Document x86 uses a linked list of pgds

From: "Matthew Wilcox (Oracle)" <willy@...radead.org>

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@...radead.org>
---
 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