linux-kernel - [PATCH v6 2/4] rcu: shrinker for lazy rcu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20220922220104.2446868-3-joel@joelfernandes.org>
Date:   Thu, 22 Sep 2022 22:01:02 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rushikesh.s.kadam@...el.com,
        urezki@...il.com, neeraj.iitr10@...il.com, frederic@...nel.org,
        paulmck@...nel.org, rostedt@...dmis.org,
        Vineeth Pillai <vineeth@...byteword.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH v6 2/4] rcu: shrinker for lazy rcu

From: Vineeth Pillai <vineeth@...byteword.org>

The shrinker is used to speed up the free'ing of memory potentially held
by RCU lazy callbacks. RCU kernel module test cases show this to be
effective. Test is introduced in a later patch.

Signed-off-by: Vineeth Pillai <vineeth@...byteword.org>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree_nocb.h | 52 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 661c685aba3f..1a182b9c4f6c 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1332,6 +1332,55 @@ int rcu_nocb_cpu_offload(int cpu)
 }
 EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
 
+static unsigned long
+lazy_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 rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+		count +=  READ_ONCE(rdp->lazy_len);
+	}
+
+	return count ? count : SHRINK_EMPTY;
+}
+
+static unsigned long
+lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	int cpu;
+	unsigned long flags;
+	unsigned long count = 0;
+
+	/* Snapshot count of all CPUs */
+	for_each_possible_cpu(cpu) {
+		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+		int _count = READ_ONCE(rdp->lazy_len);
+
+		if (_count == 0)
+			continue;
+		rcu_nocb_lock_irqsave(rdp, flags);
+		WRITE_ONCE(rdp->lazy_len, 0);
+		rcu_nocb_unlock_irqrestore(rdp, flags);
+		wake_nocb_gp(rdp, false);
+		sc->nr_to_scan -= _count;
+		count += _count;
+		if (sc->nr_to_scan <= 0)
+			break;
+	}
+	return count ? count : SHRINK_STOP;
+}
+
+static struct shrinker lazy_rcu_shrinker = {
+	.count_objects = lazy_rcu_shrink_count,
+	.scan_objects = lazy_rcu_shrink_scan,
+	.batch = 0,
+	.seeks = DEFAULT_SEEKS,
+};
+
 void __init rcu_init_nohz(void)
 {
 	int cpu;
@@ -1362,6 +1411,9 @@ void __init rcu_init_nohz(void)
 	if (!rcu_state.nocb_is_setup)
 		return;
 
+	if (register_shrinker(&lazy_rcu_shrinker, "rcu-lazy"))
+		pr_err("Failed to register lazy_rcu shrinker!\n");
+
 	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
 		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
 		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
-- 
2.37.3.998.g577e59143f-goog