linux-kernel - [PATCH RFC 3/3] mm: remove folio_test_anon(folio)==false path in __folio_add_anon

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Date: Thu, 13 Jun 2024 12:07:21 +1200
From: Barry Song <21cnbao@...il.com>
To: david@...hat.com,
	akpm@...ux-foundation.org,
	linux-mm@...ck.org
Cc: chrisl@...nel.org,
	linux-kernel@...r.kernel.org,
	mhocko@...e.com,
	ryan.roberts@....com,
	baolin.wang@...ux.alibaba.com,
	yosryahmed@...gle.com,
	shy828301@...il.com,
	surenb@...gle.com,
	v-songbaohua@...o.com,
	willy@...radead.org,
	ying.huang@...el.com,
	yuzhao@...gle.com
Subject: [PATCH RFC 3/3] mm: remove folio_test_anon(folio)==false path in __folio_add_anon_rmap()

From: Barry Song <v-songbaohua@...o.com>

The folio_test_anon(folio)==false case within do_swap_page() has been
relocated to folio_add_new_anon_rmap(). Additionally, two other callers
consistently pass anonymous folios.

stack 1:
remove_migration_pmd
   -> folio_add_anon_rmap_pmd
     -> __folio_add_anon_rmap

stack 2:
__split_huge_pmd_locked
   -> folio_add_anon_rmap_ptes
      -> __folio_add_anon_rmap

__folio_add_anon_rmap() only needs to handle the cases
folio_test_anon(folio)==true now.

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
 mm/rmap.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index e612d999811a..e84c706c8241 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1299,21 +1299,10 @@ static __always_inline void __folio_add_anon_rmap(struct folio *folio,
 
 	nr = __folio_add_rmap(folio, page, nr_pages, level, &nr_pmdmapped);
 
-	if (unlikely(!folio_test_anon(folio))) {
-		VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
-		/*
-		 * For a PTE-mapped large folio, we only know that the single
-		 * PTE is exclusive. Further, __folio_set_anon() might not get
-		 * folio->index right when not given the address of the head
-		 * page.
-		 */
-		VM_WARN_ON_FOLIO(folio_test_large(folio) &&
-				 level != RMAP_LEVEL_PMD, folio);
-		__folio_set_anon(folio, vma, address,
-				 !!(flags & RMAP_EXCLUSIVE));
-	} else if (likely(!folio_test_ksm(folio))) {
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+	if (likely(!folio_test_ksm(folio)))
 		__page_check_anon_rmap(folio, page, vma, address);
-	}
 
 	__folio_mod_stat(folio, nr, nr_pmdmapped);
 
-- 
2.34.1