linux-kernel - [RFC PATCH 16/31] mm: thp: check compound_mapcount of PMD-mapped PUD THPs at free time.

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Message-Id: <20190215220856.29749-17-zi.yan@sent.com>
Date:   Fri, 15 Feb 2019 14:08:41 -0800
From:   Zi Yan <zi.yan@...t.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        John Hubbard <jhubbard@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Nitin Gupta <nigupta@...dia.com>,
        David Nellans <dnellans@...dia.com>, Zi Yan <ziy@...dia.com>
Subject: [RFC PATCH 16/31] mm: thp: check compound_mapcount of PMD-mapped PUD THPs at free time.

From: Zi Yan <ziy@...dia.com>

PMD mappings on a PUD THP should be zero when the page is freed.

Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/page_alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dbcccc022b30..b87a2ca0a97c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1007,8 +1007,10 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
 		/* sub_compound_map_ptr store here */
 		if (compound_order(head_page) == HPAGE_PUD_ORDER &&
 			(page - head_page) % HPAGE_PMD_NR == 3) {
-			if (unlikely(atomic_read(&page->compound_mapcount) != -1))
+			if (unlikely(atomic_read(&page->compound_mapcount) != -1)) {
+				pr_err("sub_compound_mapcount: %d\n", atomic_read(&page->compound_mapcount) + 1);
 				bad_page(page, "nonzero sub_compound_mapcount", 0);
+			}
 			break;
 		}
 		if (page->mapping != TAIL_MAPPING) {
-- 
2.20.1