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From:   Peter Xu <peterx@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Mike Kravetz <mike.kravetz@oracle.com>, peterx@redhat.com,
        Jerome Glisse <jglisse@redhat.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Hugh Dickins <hughd@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>
Subject: [PATCH RFC 01/30] mm/thp: Simplify copying of huge zero page pmd when fork
Date:   Fri, 15 Jan 2021 12:08:38 -0500
Message-Id: <20210115170907.24498-2-peterx@redhat.com>
In-Reply-To: <20210115170907.24498-1-peterx@redhat.com>
References: <20210115170907.24498-1-peterx@redhat.com>
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Huge zero page is handled in a special path in copy_huge_pmd(), however it
should share most codes with a normal thp page.  Trying to share more code with
it by removing the special path.  The only leftover so far is the huge zero
page refcounting (mm_get_huge_zero_page()), because that's separately done with
a global counter.

This prepares for a future patch to modify the huge pmd to be installed, so
that we don't need to duplicate it explicitly into huge zero page case too.

Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/huge_memory.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ec2bb93f7431..b64ad1947900 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1058,17 +1058,13 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	 * a page table.
 	 */
 	if (is_huge_zero_pmd(pmd)) {
-		struct page *zero_page;
 		/*
 		 * get_huge_zero_page() will never allocate a new page here,
 		 * since we already have a zero page to copy. It just takes a
 		 * reference.
 		 */
-		zero_page = mm_get_huge_zero_page(dst_mm);
-		set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
-				zero_page);
-		ret = 0;
-		goto out_unlock;
+		mm_get_huge_zero_page(dst_mm);
+		goto out_zero_page;
 	}
 
 	src_page = pmd_page(pmd);
@@ -1094,6 +1090,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	get_page(src_page);
 	page_dup_rmap(src_page, true);
 	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+out_zero_page:
 	mm_inc_nr_ptes(dst_mm);
 	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 
-- 
2.26.2