mm: multigenerational lru: add /sys/kernel/mm/lru_gen/min_ttl_ms

Add /sys/kernel/mm/lru_gen/min_ttl_ms to protect generations that are
younger than the value of this file. The multigenerational lru will
not consider those generations. And if there are no older generations
left, it will oom kill. The default value 0 means this feature is
disabled.

Signed-off-by: Yu Zhao <yuzhao@google.com>

mm/memcontrol.c

@@ -6002,7 +6002,7 @@ static void mem_cgroup_attach(struct cgroup_taskset *tset)
 	struct task_struct *task = NULL;
 
 	cgroup_taskset_for_each_leader(task, css, tset)
-		;
+		break;
 
 	if (!task)
 		return;

mm/vmscan.c

@@ -4333,6 +4333,8 @@ static int get_swappiness(struct lruvec *lruvec)
 	return swappiness;
 }
 
+static DEFINE_RATELIMIT_STATE(lru_gen_min_ttl, 0, 1);
+
 static unsigned long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 				    int swappiness)
 {
@@ -4362,6 +4364,11 @@ static unsigned long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *
 	nr_gens = max_nr_gens(max_seq, min_seq, swappiness);
 
 	if (current_is_kswapd()) {
+		gen = lru_gen_from_seq(max_seq - nr_gens + 1);
+		if (time_is_before_eq_jiffies(READ_ONCE(lrugen->timestamps[gen]) +
+					      READ_ONCE(lru_gen_min_ttl.interval)))
+			sc->file_is_tiny = 0;
+
 		/* leave the work to age_lru_gens() */
 		if (nr_gens == MIN_NR_GENS)
 			return 0;
@@ -4466,6 +4473,21 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
 
 	VM_BUG_ON(!current_is_kswapd());
 
+	if (sc->file_is_tiny && READ_ONCE(lru_gen_min_ttl.interval) &&
+	    __ratelimit(&lru_gen_min_ttl)) {
+		struct oom_control oc = {
+			.gfp_mask = sc->gfp_mask,
+			.order = sc->order,
+		};
+
+		if (mutex_trylock(&oom_lock)) {
+			out_of_memory(&oc);
+			mutex_unlock(&oom_lock);
+		}
+	}
+
+	sc->file_is_tiny = 1;
+
 	if (!mem_cgroup_disabled() && !sc->force_deactivate) {
 		/* we may clear this later in get_nr_to_scan() */
 		sc->force_deactivate = 1;
@@ -4730,6 +4752,29 @@ static struct kobj_attribute lru_gen_spread_attr = __ATTR(
 	spread, 0644, show_lru_gen_spread, store_lru_gen_spread
 );
 
+static ssize_t show_lru_gen_min_ttl(struct kobject *kobj, struct kobj_attribute *attr,
+				    char *buf)
+{
+	return sprintf(buf, "%u\n", jiffies_to_msecs(READ_ONCE(lru_gen_min_ttl.interval)));
+}
+
+static ssize_t store_lru_gen_min_ttl(struct kobject *kobj, struct kobj_attribute *attr,
+				     const char *buf, size_t len)
+{
+	unsigned int msecs;
+
+	if (kstrtouint(buf, 10, &msecs))
+		return -EINVAL;
+
+	WRITE_ONCE(lru_gen_min_ttl.interval, msecs_to_jiffies(msecs));
+
+	return len;
+}
+
+static struct kobj_attribute lru_gen_min_ttl_attr = __ATTR(
+	min_ttl_ms, 0644, show_lru_gen_min_ttl, store_lru_gen_min_ttl
+);
+
 static ssize_t show_lru_gen_enabled(struct kobject *kobj, struct kobj_attribute *attr,
 				    char *buf)
 {
@@ -4755,6 +4800,7 @@ static struct kobj_attribute lru_gen_enabled_attr = __ATTR(
 
 static struct attribute *lru_gen_attrs[] = {
 	&lru_gen_spread_attr.attr,
+	&lru_gen_min_ttl_attr.attr,
 	&lru_gen_enabled_attr.attr,
 	NULL
 };