> On Fri, May 13, 2022 at 04:53:05PM +0200, Uladzislau Rezki wrote:
> > > monitor_todo is not needed as the work struct already tracks if work is
> > > pending. Just use that to know if work is pending using
> > > delayed_work_pending() helper.
> > >
> > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > > ---
> > > kernel/rcu/tree.c | 22 +++++++---------------
> > > 1 file changed, 7 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 3baf29014f86..3828ac3bf1c4 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -3155,7 +3155,6 @@ struct kfree_rcu_cpu_work {
> > > * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
> > > * @lock: Synchronize access to this structure
> > > * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
> > > - * @monitor_todo: Tracks whether a @monitor_work delayed work is pending
> > > * @initialized: The @rcu_work fields have been initialized
> > > * @count: Number of objects for which GP not started
> > > * @bkvcache:
> > > @@ -3180,7 +3179,6 @@ struct kfree_rcu_cpu {
> > > struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
> > > raw_spinlock_t lock;
> > > struct delayed_work monitor_work;
> > > - bool monitor_todo;
> > > bool initialized;
> > > int count;
> > >
> > > @@ -3416,9 +3414,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
> > > // of the channels that is still busy we should rearm the
> > > // work to repeat an attempt. Because previous batches are
> > > // still in progress.
> > > - if (!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head)
> > > - krcp->monitor_todo = false;
> > > - else
> > > + if (krcp->bkvhead[0] || krcp->bkvhead[1] || krcp->head)
>
Can we place those three checks into separate inline function because
it is used in two places: krc_needs_offload()?
> > > schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> > >
> > > raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > > @@ -3607,10 +3603,8 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > >
> > > // Set timer to drain after KFREE_DRAIN_JIFFIES.
> > > if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
> > > - !krcp->monitor_todo) {
> > > - krcp->monitor_todo = true;
> > > + !delayed_work_pending(&krcp->monitor_work))
>
I think checking weather it is pending or not does not make much sense.
schedule_delayed_work() checks inside if the work can be queued.
> > > schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> > > - }
> > >
> > > unlock_return:
> > > krc_this_cpu_unlock(krcp, flags);
> > > @@ -3685,14 +3679,12 @@ void __init kfree_rcu_scheduler_running(void)
> > > struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
> > >
> > > raw_spin_lock_irqsave(&krcp->lock, flags);
> > > - if ((!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head) ||
> > > - krcp->monitor_todo) {
> > > - raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > > - continue;
> > > + if (krcp->bkvhead[0] || krcp->bkvhead[1] || krcp->head) {
Same here. Move to the separate function, IMHO makes sense.
> > > + if (delayed_work_pending(&krcp->monitor_work)) {
Same here. Should we check it here?
> > > + schedule_delayed_work_on(cpu, &krcp->monitor_work,
> > > + KFREE_DRAIN_JIFFIES);
> > > + }
> > > }
> > > - krcp->monitor_todo = true;
> > > - schedule_delayed_work_on(cpu, &krcp->monitor_work,
> > > - KFREE_DRAIN_JIFFIES);
> > > raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > > }
> > > }
> > > --
> > >
> > Looks good to me from the first glance, but let me know to have a look
> > at it more closely.
>
> Thanks, I appreciate it.
>
One change in design after this patch is a drain work can be queued even
though there is already nothing to drain. I do not find it as a big issue
because it will just bail out. So i tend to simplification.
The monitor_todo guarantees that kvfree_rcu() caller will not schedule
any work until "monitor work" completes its job and if there is still to
do something there it rearms itself.
--
Uladzsialu Rezki
