[RFC PATCH 1/2] mm/gup: move pinned pages to unevictable list to avoid meaningless scan

[Jinjiang Tu <tujinjiang@huawei.com>]

To avoid meaningless scan during memory reclaim, this patch moves pinned
pages to unevictable list to avoid meaningless scan during memory reclaim.
Update folio_evictable() to check if the folio is pinned. If the folio is
pinned, the function returns false. The vmscan code will put the folio to
inevictable list when scanning the folio, so each pinned page will be
scanned at most once. When the folio is unpinned, check if the folio can
be put back to inactive/active list by calling folio_evictable().

Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
---
 mm/gup.c      | 13 +++++++++++++
 mm/internal.h |  2 +-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 6e2f9e9d6537..ca82e1bc6826 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -200,6 +200,19 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
 
 	if (!put_devmap_managed_page_refs(&folio->page, refs))
 		folio_put_refs(folio, refs);
+
+	if (folio_test_unevictable(folio) && folio_evictable(folio)) {
+		struct lruvec *lruvec = folio_lruvec_lock_irq(folio);
+
+		lruvec_del_folio(lruvec, folio);
+		folio_clear_unevictable(folio);
+		lruvec_add_folio(lruvec, folio);
+		folio_set_lru(folio);
+		__count_vm_events(UNEVICTABLE_PGRESCUED,
+			folio_nr_pages(folio));
+
+		unlock_page_lruvec_irq(lruvec);
+	}
 }
 
 /**
diff --git a/mm/internal.h b/mm/internal.h
index 8ed127c1c808..9ce158de40cf 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -154,7 +154,7 @@ static inline bool folio_evictable(struct folio *folio)
 	/* Prevent address_space of inode and swap cache from being freed */
 	rcu_read_lock();
 	ret = !mapping_unevictable(folio_mapping(folio)) &&
-			!folio_test_mlocked(folio);
+			!folio_test_mlocked(folio) && !folio_maybe_dma_pinned(folio);
 	rcu_read_unlock();
 	return ret;
 }
-- 
2.25.1