[RFC PATCH v3 12/14] mm/memcontrol: Kick async reclaim on migration and folio replacement

Memcg tier charges are now transferred during folio migrations, but
this still leaves forced charges and unenforced paths like folio
replacement, hugetlb migration, and memory hotplug.

Forced charges can and should not be enforced by synchronous reclaim,
but if soft limits are set, we can kick async reclaimers to try and
bring the usage below the high memcg tier limit.

No-op unless the system has tiered memcg limits enabled.

Signed-off-by: Joshua Hahn <[email protected]>
---
 mm/memcontrol.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1161934e81380..4dce7c6fefd98 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5663,6 +5663,16 @@ void __mem_cgroup_uncharge_folios(struct folio_batch *folios)
 		uncharge_batch(&ug);
 }
 
+static void tier_kick_high(struct mem_cgroup *memcg, int slot)
+{
+	struct page_counter *tier_counter;
+
+	tier_counter = mem_cgroup_tier_counter(memcg, slot);
+	if (tier_counter && page_counter_read(tier_counter) >
+			    READ_ONCE(tier_counter->high))
+		schedule_work(&memcg->high_work);
+}
+
 /**
  * mem_cgroup_replace_folio - Charge a folio's replacement.
  * @old: Currently circulating folio.
@@ -5705,6 +5715,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
 			int slot = nid_tier_slot(folio_nid(new));
 
 			mem_cgroup_charge_tier(memcg, slot, nr_pages);
+			tier_kick_high(memcg, slot);
 		}
 		if (do_memsw_account())
 			page_counter_charge(&memcg->memsw, nr_pages);
@@ -5798,6 +5809,7 @@ void mem_cgroup_migrate(struct folio *old, struct folio *new)
 		if (old_slot != new_slot) {
 			mem_cgroup_uncharge_tier(memcg, old_slot, nr_pages);
 			mem_cgroup_charge_tier(memcg, new_slot, nr_pages);
+			tier_kick_high(memcg, new_slot);
 		}
 		rcu_read_unlock();
 	}
-- 
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