[PATCH 1/4] mm/vmscan: introduce folio_activate_locked() helper

[Zhang Peng <zippermonkey@icloud.com>]

From: Zhang Peng <bruzzhang@tencent.com>

The activate_locked label in shrink_folio_list() reclaims swap cache
when needed, marks the folio active, and updates activation statistics.
Extract this block into folio_activate_locked() so it can be reused.

Replace the active-folio BUG with a warning so a bad caller is reported
without taking down the system. Otherwise, there is no functional change.

Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Zhang Peng <bruzzhang@tencent.com>
---
 mm/vmscan.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index e200ce3eb056..c6beca88079a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1155,6 +1155,28 @@ static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)
 	return false;
 }
 
+/* Activate an isolated, locked folio and account the activation. */
+static void folio_activate_locked(struct folio *folio,
+		struct reclaim_stat *stat)
+{
+	unsigned int nr_pages = folio_nr_pages(folio);
+
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
+
+	/* Not a candidate for swapping, so reclaim swap space. */
+	if (folio_test_swapcache(folio) &&
+	    (mem_cgroup_swap_full(folio) || folio_test_mlocked(folio)))
+		folio_free_swap(folio);
+	if (!folio_test_mlocked(folio)) {
+		int type = folio_is_file_lru(folio);
+
+		folio_set_active(folio);
+		stat->nr_activate[type] += nr_pages;
+		count_memcg_folio_events(folio, PGACTIVATE, nr_pages);
+	}
+}
+
 /*
  * shrink_folio_list() returns the number of reclaimed pages
  */
@@ -1623,24 +1645,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 activate_locked_split:
 		/*
 		 * The tail pages that are failed to add into swap cache
-		 * reach here.  Fixup nr_scanned and nr_pages.
+		 * reach here.  Fixup nr_scanned.
 		 */
-		if (nr_pages > 1) {
+		if (nr_pages > 1)
 			sc->nr_scanned -= (nr_pages - 1);
-			nr_pages = 1;
-		}
 activate_locked:
-		/* Not a candidate for swapping, so reclaim swap space. */
-		if (folio_test_swapcache(folio) &&
-		    (mem_cgroup_swap_full(folio) || folio_test_mlocked(folio)))
-			folio_free_swap(folio);
-		VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
-		if (!folio_test_mlocked(folio)) {
-			int type = folio_is_file_lru(folio);
-			folio_set_active(folio);
-			stat->nr_activate[type] += nr_pages;
-			count_memcg_folio_events(folio, PGACTIVATE, nr_pages);
-		}
+		folio_activate_locked(folio, stat);
 keep_locked:
 		folio_unlock(folio);
 keep:

-- 
2.55.0