> On ChromeOS, using this with the increased timeout, we see that we almost always
> never need to initiate a new grace period. Testing also shows this frees large
> amounts of unreclaimed memory, under intense kfree_rcu() pressure.
>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> v1->v2: Same logic but use polled grace periods instead of sampling gp_seq.
>
> kernel/rcu/tree.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 591187b6352e..ed41243f7a49 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2935,6 +2935,7 @@ struct kfree_rcu_cpu_work {
>
> /**
> * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
> + * @gp_snap: The GP snapshot recorded at the last scheduling of monitor work.
> * @head: List of kfree_rcu() objects not yet waiting for a grace period
> * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
> * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
> @@ -2964,6 +2965,7 @@ struct kfree_rcu_cpu {
> struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
> raw_spinlock_t lock;
> struct delayed_work monitor_work;
> + unsigned long gp_snap;
> bool initialized;
> int count;
>
> @@ -3167,6 +3169,7 @@ schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
> mod_delayed_work(system_wq, &krcp->monitor_work, delay);
> return;
> }
> + krcp->gp_snap = get_state_synchronize_rcu();
> queue_delayed_work(system_wq, &krcp->monitor_work, delay);
> }
>
How do you guarantee a full grace period for objects which proceed
to be placed into an input stream that is not yet detached?
>
> @@ -3217,7 +3220,10 @@ static void kfree_rcu_monitor(struct work_struct *work)
> // be that the work is in the pending state when
> // channels have been detached following by each
> // other.
> - queue_rcu_work(system_wq, &krwp->rcu_work);
> + if (poll_state_synchronize_rcu(krcp->gp_snap))
> + queue_work(system_wq, &krwp->rcu_work.work);
> + else
> + queue_rcu_work(system_wq, &krwp->rcu_work);
> }
>
Why do you want to queue a work over RCU-core?
1.
call_rcu()
-> queue_work();
-> do reclaim
if it can be improved and simplified as:
2.
queue_work();
-> cond_synchronize_rcu(), do reclaim
Could you please clarify it?
--
Uladzislau Rezki
