linux-kernel - [PATCH 4/4] mm/rmap: try_to_migrate() skip zone_device !device

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Date:   Wed, 7 Jul 2021 13:13:33 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Hugh Dickins <hughd@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Christoph Hellwig <hch@....de>, Yang Shi <shy828301@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 4/4] mm/rmap: try_to_migrate() skip zone_device
 !device_private

I know nothing about zone_device pages and !device_private pages; but
if try_to_migrate_one() will do nothing for them, then it's better that
try_to_migrate() filter them first, than trawl through all their vmas.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 mm/rmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 1235368f0628..795f9d5f8386 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1703,9 +1703,6 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
 	struct mmu_notifier_range range;
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
 
-	if (is_zone_device_page(page) && !is_device_private_page(page))
-		return true;
-
 	/*
 	 * When racing against e.g. zap_pte_range() on another cpu,
 	 * in between its ptep_get_and_clear_full() and page_remove_rmap(),
@@ -1944,6 +1941,9 @@ void try_to_migrate(struct page *page, enum ttu_flags flags)
 					TTU_SYNC)))
 		return;
 
+	if (is_zone_device_page(page) && !is_device_private_page(page))
+		return;
+
 	/*
 	 * During exec, a temporary VMA is setup and later moved.
 	 * The VMA is moved under the anon_vma lock but not the
-- 
2.26.2