[RFC v1 4/5] mm/slab: Copy a function of kvfree_rcu() initialization

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

As a final step an initialization of kvfree_rcu() functionality is
copied into slab_common.c from the tree.c file as well as shrinker
related code.

The function is temporary marked as "__maybe_unused" to eliminate
a compiler warnings.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/slab_common.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index e7e1d5b5f31b..cffc96bd279a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1940,3 +1940,94 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
 
 	return true;
 }
+
+static unsigned long
+kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	int cpu;
+	unsigned long count = 0;
+
+	/* Snapshot count of all CPUs */
+	for_each_possible_cpu(cpu) {
+		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+		count += krc_count(krcp);
+		count += READ_ONCE(krcp->nr_bkv_objs);
+		atomic_set(&krcp->backoff_page_cache_fill, 1);
+	}
+
+	return count == 0 ? SHRINK_EMPTY : count;
+}
+
+static unsigned long
+kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	int cpu, freed = 0;
+
+	for_each_possible_cpu(cpu) {
+		int count;
+		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+		count = krc_count(krcp);
+		count += drain_page_cache(krcp);
+		kfree_rcu_monitor(&krcp->monitor_work.work);
+
+		sc->nr_to_scan -= count;
+		freed += count;
+
+		if (sc->nr_to_scan <= 0)
+			break;
+	}
+
+	return freed == 0 ? SHRINK_STOP : freed;
+}
+
+static void __init __maybe_unused
+kfree_rcu_batch_init(void)
+{
+	int cpu;
+	int i, j;
+	struct shrinker *kfree_rcu_shrinker;
+
+	/* Clamp it to [0:100] seconds interval. */
+	if (rcu_delay_page_cache_fill_msec < 0 ||
+		rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
+
+		rcu_delay_page_cache_fill_msec =
+			clamp(rcu_delay_page_cache_fill_msec, 0,
+				(int) (100 * MSEC_PER_SEC));
+
+		pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
+			rcu_delay_page_cache_fill_msec);
+	}
+
+	for_each_possible_cpu(cpu) {
+		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+		for (i = 0; i < KFREE_N_BATCHES; i++) {
+			INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
+			krcp->krw_arr[i].krcp = krcp;
+
+			for (j = 0; j < FREE_N_CHANNELS; j++)
+				INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]);
+		}
+
+		for (i = 0; i < FREE_N_CHANNELS; i++)
+			INIT_LIST_HEAD(&krcp->bulk_head[i]);
+
+		INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
+		INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
+		krcp->initialized = true;
+	}
+
+	kfree_rcu_shrinker = shrinker_alloc(0, "rcu-slab-kfree");
+	if (!kfree_rcu_shrinker) {
+		pr_err("Failed to allocate kfree_rcu() shrinker!\n");
+		return;
+	}
+
+	kfree_rcu_shrinker->count_objects = kfree_rcu_shrink_count;
+	kfree_rcu_shrinker->scan_objects = kfree_rcu_shrink_scan;
+
+	shrinker_register(kfree_rcu_shrinker);
+}
-- 
2.39.5