linux-kernel - [PATCH 2/7] mm: Move pt

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Date:   Tue, 28 Apr 2020 12:44:44 -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 2/7] mm: Move pt_mm within struct page

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

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@...radead.org>
---
 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