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BACKPORT: rcu: Shrinker for lazy rcu

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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@bitbyteword.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
(cherry picked from commit c945b4da7a448a9a56becc5a8745d942b2b83d3c)

Conflicts:
   kernel/rcu/tree_nocb.h

Trivial conflict due to: "rcu/nocb: Add an option to offload all CPUs on boot"

Bug: 258241771
Signed-off-by: Joel Fernandes <joelaf@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4909032
Reviewed-by: Vineeth Pillai <vineethrp@google.com>
Signed-off-by: Qais Yousef <qyousef@google.com>
Change-Id: I6a73a9dae79ff35feca37abe2663e55a0f46dda8
This commit is contained in:
Vineeth Pillai 2022-10-16 16:22:56 +00:00 committed by Todd Kjos
parent 4957579439
commit c570c8fea3
1 changed files with 52 additions and 0 deletions
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52
kernel/rcu/tree_nocb.h
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@ -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;
@ -1354,6 +1403,9 @@ void __init rcu_init_nohz(void)
if (offload_all)
cpumask_setall(rcu_nocb_mask);
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,