rcuscale: Add laziness and kfree tests

This commit adds 2 tests to rcuscale.  The first one is a startup test
to check whether we are not too lazy or too hard working.  The second
one causes kfree_rcu() itself to use call_rcu() and checks memory
pressure. Testing indicates that the new call_rcu() keeps memory pressure
under control roughly as well as does kfree_rcu().

[ paulmck: Apply checkpatch feedback. ]

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 3ef02d4a810855f9fdc2befcc251e6134da0b8f4..3baded807a6162a0fefb6d8c842f87a2568e97cd 100644 (file)
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -95,6 +95,7 @@ torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
 torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
 torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() scale test?");
 torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate.");
+torture_param(int, kfree_by_call_rcu, 0, "Use call_rcu() to emulate kfree_rcu()?");
 
 static char *scale_type = "rcu";
 module_param(scale_type, charp, 0444);
@@ -659,6 +660,14 @@ struct kfree_obj {
        struct rcu_head rh;
 };
 
+/* Used if doing RCU-kfree'ing via call_rcu(). */
+static void kfree_call_rcu(struct rcu_head *rh)
+{
+       struct kfree_obj *obj = container_of(rh, struct kfree_obj, rh);
+
+       kfree(obj);
+}
+
 static int
 kfree_scale_thread(void *arg)
 {
@@ -696,6 +705,11 @@ kfree_scale_thread(void *arg)
                        if (!alloc_ptr)
                                return -ENOMEM;
 
+                       if (kfree_by_call_rcu) {
+                               call_rcu(&(alloc_ptr->rh), kfree_call_rcu);
+                               continue;
+                       }
+
                        // By default kfree_rcu_test_single and kfree_rcu_test_double are
                        // initialized to false. If both have the same value (false or true)
                        // both are randomly tested, otherwise only the one with value true
@@ -767,11 +781,58 @@ kfree_scale_shutdown(void *arg)
        return -EINVAL;
 }
 
+// Used if doing RCU-kfree'ing via call_rcu().
+static unsigned long jiffies_at_lazy_cb;
+static struct rcu_head lazy_test1_rh;
+static int rcu_lazy_test1_cb_called;
+static void call_rcu_lazy_test1(struct rcu_head *rh)
+{
+       jiffies_at_lazy_cb = jiffies;
+       WRITE_ONCE(rcu_lazy_test1_cb_called, 1);
+}
+
 static int __init
 kfree_scale_init(void)
 {
-       long i;
        int firsterr = 0;
+       long i;
+       unsigned long jif_start;
+       unsigned long orig_jif;
+
+       // Also, do a quick self-test to ensure laziness is as much as
+       // expected.
+       if (kfree_by_call_rcu && !IS_ENABLED(CONFIG_RCU_LAZY)) {
+               pr_alert("CONFIG_RCU_LAZY is disabled, falling back to kfree_rcu() for delayed RCU kfree'ing\n");
+               kfree_by_call_rcu = 0;
+       }
+
+       if (kfree_by_call_rcu) {
+               /* do a test to check the timeout. */
+               orig_jif = rcu_lazy_get_jiffies_till_flush();
+
+               rcu_lazy_set_jiffies_till_flush(2 * HZ);
+               rcu_barrier();
+
+               jif_start = jiffies;
+               jiffies_at_lazy_cb = 0;
+               call_rcu(&lazy_test1_rh, call_rcu_lazy_test1);
+
+               smp_cond_load_relaxed(&rcu_lazy_test1_cb_called, VAL == 1);
+
+               rcu_lazy_set_jiffies_till_flush(orig_jif);
+
+               if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) {
+                       pr_alert("ERROR: call_rcu() CBs are not being lazy as expected!\n");
+                       WARN_ON_ONCE(1);
+                       return -1;
+               }
+
+               if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start > 3 * HZ)) {
+                       pr_alert("ERROR: call_rcu() CBs are being too lazy!\n");
+                       WARN_ON_ONCE(1);
+                       return -1;
+               }
+       }
 
        kfree_nrealthreads = compute_real(kfree_nthreads);
        /* Start up the kthreads. */
@@ -784,7 +845,9 @@ kfree_scale_init(void)
                schedule_timeout_uninterruptible(1);
        }
 
-       pr_alert("kfree object size=%zu\n", kfree_mult * sizeof(struct kfree_obj));
+       pr_alert("kfree object size=%zu, kfree_by_call_rcu=%d\n",
+                       kfree_mult * sizeof(struct kfree_obj),
+                       kfree_by_call_rcu);
 
        kfree_reader_tasks = kcalloc(kfree_nrealthreads, sizeof(kfree_reader_tasks[0]),
                               GFP_KERNEL);