From c945b4da7a448a9a56becc5a8745d942b2b83d3c Mon Sep 17 00:00:00 2001 From: Vineeth Pillai Date: Sun, 16 Oct 2022 16:22:56 +0000 Subject: [PATCH] rcu: Shrinker for lazy rcu 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 Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- 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 213daf81c057..9e1c8caec5ce 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1312,6 +1312,55 @@ 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; @@ -1342,6 +1391,9 @@ 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,