linux-kernel - [RFC PATCH 17/31] mm: thp: split properly PMD-mapped PUD THP to PTE-mapped PUD THP.

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Message-Id: <20190215220856.29749-18-zi.yan@sent.com>
Date:   Fri, 15 Feb 2019 14:08:42 -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 17/31] mm: thp: split properly PMD-mapped PUD THP to PTE-mapped PUD THP.

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

Page count increase needs to goto the head of the PUD page.

Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/huge_memory.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5f83f4c5eac7..bbdbc9ae06bf 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3198,7 +3198,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long haddr, bool freeze)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	struct page *page;
+	struct page *page, *head;
 	pgtable_t pgtable;
 	pmd_t old_pmd, _pmd;
 	bool young, write, soft_dirty, pmd_migration = false;
@@ -3285,7 +3285,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		soft_dirty = pmd_soft_dirty(old_pmd);
 	}
 	VM_BUG_ON_PAGE(!page_count(page), page);
-	page_ref_add(page, HPAGE_PMD_NR - 1);
+	head = compound_head(page);
+	page_ref_add(head, HPAGE_PMD_NR - 1);
 
 	/*
 	 * Withdraw the table only after we mark the pmd entry invalid.
-- 
2.20.1