linux-kernel - [PATCH v5 26/39] mm: Fix total_mapcount assumption of page size

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Message-Id: <20200529025824.32296-27-willy@infradead.org>
Date:   Thu, 28 May 2020 19:58:11 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: [PATCH v5 26/39] mm: Fix total_mapcount assumption of page size

From: "Kirill A. Shutemov" <kirill@...temov.name>

File THPs may now be of arbitrary order.

Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 mm/huge_memory.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7a5e2b470bc7..15a86b06befc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2668,7 +2668,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 
 int total_mapcount(struct page *page)
 {
-	int i, compound, ret;
+	int i, compound, nr, ret;
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
 
@@ -2676,16 +2676,17 @@ int total_mapcount(struct page *page)
 		return atomic_read(&page->_mapcount) + 1;
 
 	compound = compound_mapcount(page);
+	nr = compound_nr(page);
 	if (PageHuge(page))
 		return compound;
 	ret = compound;
-	for (i = 0; i < HPAGE_PMD_NR; i++)
+	for (i = 0; i < nr; i++)
 		ret += atomic_read(&page[i]._mapcount) + 1;
 	/* File pages has compound_mapcount included in _mapcount */
 	if (!PageAnon(page))
-		return ret - compound * HPAGE_PMD_NR;
+		return ret - compound * nr;
 	if (PageDoubleMap(page))
-		ret -= HPAGE_PMD_NR;
+		ret -= nr;
 	return ret;
 }
 
-- 
2.26.2