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Date:   Tue, 8 Jun 2021 21:27:45 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Yang Shi <shy828301@gmail.com>,
        Wang Yugui <wangyugui@e16-tech.com>,
        Matthew Wilcox <willy@infradead.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Alistair Popple <apopple@nvidia.com>,
        Ralph Campbell <rcampbell@nvidia.com>, Zi Yan <ziy@nvidia.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Minchan Kim <minchan@kernel.org>, Jue Wang <juew@google.com>,
        Peter Xu <peterx@redhat.com>, Jan Kara <jack@suse.cz>,
        Shakeel Butt <shakeelb@google.com>,
        Oscar Salvador <osalvador@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v2 09/10] mm/thp: remap_page() is only needed on anonymous
 THP
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THP splitting's unmap_page() only sets TTU_SPLIT_FREEZE when PageAnon,
and migration entries are only inserted when TTU_MIGRATION (unused here)
or TTU_SPLIT_FREEZE is set: so it's just a waste of time for remap_page()
to search for migration entries to remove when !PageAnon.

Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/huge_memory.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6d2a0119fc58..319a1a078451 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2355,6 +2355,7 @@ static void unmap_page(struct page *page)
 
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 
+	/* If TTU_SPLIT_FREEZE is ever extended to file, update remap_page() */
 	if (PageAnon(page))
 		ttu_flags |= TTU_SPLIT_FREEZE;
 
@@ -2366,6 +2367,10 @@ static void unmap_page(struct page *page)
 static void remap_page(struct page *page, unsigned int nr)
 {
 	int i;
+
+	/* If TTU_SPLIT_FREEZE is ever extended to file, remove this check */
+	if (!PageAnon(page))
+		return;
 	if (PageTransHuge(page)) {
 		remove_migration_ptes(page, page, true);
 	} else {
-- 
2.26.2