[RFC PATCH 2/8] mm: vmscan: add lruvec_for_each_list() helper

[Yosry Ahmed <yosryahmed@google.com>]

This helper is used to provide a callback to be called for each lruvec
list. This abstracts different lruvec implementations (MGLRU vs. classic
LRUs). The helper is used by a following commit to iterate all folios in
all LRUs lists for memcg recharging.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
 include/linux/swap.h |  8 ++++++++
 mm/vmscan.c          | 28 ++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 456546443f1f..c0621deceb03 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -406,6 +406,14 @@ extern void lru_cache_add_inactive_or_unevictable(struct page *page,
 						struct vm_area_struct *vma);
 
 /* linux/mm/vmscan.c */
+typedef bool (*lruvec_list_fn_t)(struct lruvec *lruvec,
+				 struct list_head *list,
+				 enum lru_list lru,
+				 void *arg);
+extern void lruvec_for_each_list(struct lruvec *lruvec,
+				 lruvec_list_fn_t fn,
+				 void *arg);
+
 extern unsigned long zone_reclaimable_pages(struct zone *zone);
 extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 					gfp_t gfp_mask, nodemask_t *mask);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1080209a568b..e7956000a3b6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -6254,6 +6254,34 @@ static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control *
 
 #endif /* CONFIG_LRU_GEN */
 
+/*
+ * lruvec_for_each_list - make a callback for every folio list in the lruvec
+ * @lruvec: the lruvec to iterate lists in
+ * @fn: the callback to make for each list, iteration stops if it returns true
+ * @arg: argument to pass to @fn
+ */
+void lruvec_for_each_list(struct lruvec *lruvec, lruvec_list_fn_t fn, void *arg)
+{
+	enum lru_list lru;
+
+#ifdef CONFIG_LRU_GEN
+	if (lru_gen_enabled()) {
+		int gen, type, zone;
+
+		for_each_gen_type_zone(gen, type, zone) {
+			lru = type * LRU_INACTIVE_FILE;
+			if (fn(lruvec, &lruvec->lrugen.folios[gen][type][zone],
+			       lru, arg))
+				break;
+		}
+	} else
+#endif
+		for_each_evictable_lru(lru) {
+			if (fn(lruvec, &lruvec->lists[lru], lru, arg))
+				break;
+		}
+}
+
 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
 	unsigned long nr[NR_LRU_LISTS];
-- 
2.41.0.255.g8b1d071c50-goog