linux-kernel - Re: [PATCH 1/2] rcu/kvfree: Remove useless monitor

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Date:   Sat, 4 Jun 2022 03:07:21 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraj.iitr10@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 1/2] rcu/kvfree: Remove useless monitor_todo flag

On Fri, Jun 03, 2022 at 11:51:34AM +0200, Uladzislau Rezki wrote:
> > On Thu, Jun 02, 2022 at 10:06:43AM +0200, Uladzislau Rezki (Sony) wrote:
> > > From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> > > 
> > > 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 schedule_delayed_work() helper.
> > > 
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > ---
> > >  kernel/rcu/tree.c | 33 ++++++++++++++++-----------------
> > >  1 file changed, 16 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 222d59299a2a..fd16c0b46d9e 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -3295,7 +3295,6 @@ 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:
> > > @@ -3320,7 +3319,6 @@ 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;
> > >  
> > > @@ -3500,6 +3498,18 @@ static void kfree_rcu_work(struct work_struct *work)
> > >  	}
> > >  }
> > >  
> > > +static bool
> > > +need_offload_krc(struct kfree_rcu_cpu *krcp)
> > > +{
> > > +	int i;
> > > +
> > > +	for (i = 0; i < FREE_N_CHANNELS; i++)
> > > +		if (krcp->bkvhead[i])
> > > +			return true;
> > > +
> > > +	return !!krcp->head;
> > > +}
> > 
> > Thanks for modifying my original patch to do this, and thanks for giving me
> > the attribution for the patch. This function is a nice addition.
> > 
> It was you who did it :) Actually the second patch depends on it therefore 
> i decided to upload it on behalf of you with slight modification hoping that
> you would not mind.

Yes I don't mind at all :) Thank you again for seeing it through!

> > For the patch in its entirety:
> > Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > 
> Thanks for the review!

Sure, any time. By the way I am out in the Carribean next week. I will catch
you all the week after.

Quick update on my side on the lazy CB stuff, I made some progress on using
the bypass lists for lazy CBs, its looking good and builds now. I fixed bug
in my code where idle loop was flushing lazy CBs on its way to idle.. I think
its probably O(workingdays) away from v2 posting assuming all goes well.

thanks,

 - Joel