[PATCH 6/6 v2] mm: Drain LRUs upon resume to userspace on nohz_full CPUs

[Frederic Weisbecker <frederic@xxxxxxxxxx>]

LRUs can be drained through several ways. One of them may add disturbances
to isolated workloads while queuing a work at any time to any target,
whether running in nohz_full mode or not.

Prevent from that on isolated tasks with defering LRUs drains upon
resuming to userspace using the isolated task work framework.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 include/linux/swap.h     | 1 +
 kernel/sched/isolation.c | 3 +++
 mm/swap.c                | 8 +++++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index b13b72645db3..a6fdcc04403e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -406,6 +406,7 @@ extern void lru_add_drain(void);
 extern void lru_add_drain_cpu(int cpu);
 extern void lru_add_drain_cpu_zone(struct zone *zone);
 extern void lru_add_drain_all(void);
+extern void lru_add_and_bh_lrus_drain(void);
 void folio_deactivate(struct folio *folio);
 void folio_mark_lazyfree(struct folio *folio);
 extern void swap_setup(void);
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index f25a5cb33c0d..1f9ec201864c 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -8,6 +8,8 @@
  *
  */
 
+#include <linux/swap.h>
+
 enum hk_flags {
 	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
 	HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
@@ -253,6 +255,7 @@ __setup("isolcpus=", housekeeping_isolcpus_setup);
 #if defined(CONFIG_NO_HZ_FULL)
 static void isolated_task_work(struct callback_head *head)
 {
+	lru_add_and_bh_lrus_drain();
 }
 
 int __isolated_task_work_queue(void)
diff --git a/mm/swap.c b/mm/swap.c
index fc8281ef4241..da1e569ee3ce 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -37,6 +37,7 @@
 #include <linux/page_idle.h>
 #include <linux/local_lock.h>
 #include <linux/buffer_head.h>
+#include <linux/sched/isolation.h>
 
 #include "internal.h"
 
@@ -376,6 +377,8 @@ static void __lru_cache_activate_folio(struct folio *folio)
 	}
 
 	local_unlock(&cpu_fbatches.lock);
+
+	isolated_task_work_queue();
 }
 
 #ifdef CONFIG_LRU_GEN
@@ -738,7 +741,7 @@ void lru_add_drain(void)
  * the same cpu. It shouldn't be a problem in !SMP case since
  * the core is only one and the locks will disable preemption.
  */
-static void lru_add_and_bh_lrus_drain(void)
+void lru_add_and_bh_lrus_drain(void)
 {
 	local_lock(&cpu_fbatches.lock);
 	lru_add_drain_cpu(smp_processor_id());
@@ -769,6 +772,9 @@ static bool cpu_needs_drain(unsigned int cpu)
 {
 	struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);
 
+	if (!housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE))
+		return false;
+
 	/* Check these in order of likelihood that they're not zero */
 	return folio_batch_count(&fbatches->lru_add) ||
 		folio_batch_count(&fbatches->lru_move_tail) ||
-- 
2.46.0