linux-kernel - Re: [PATCH 4/4] rcu: Name internal polling flag

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Message-ID: <20220317153353.GA463481@lothringen>
Date:   Thu, 17 Mar 2022 16:33:53 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 4/4] rcu: Name internal polling flag

On Thu, Mar 17, 2022 at 03:12:17PM +0530, Neeraj Upadhyay wrote:
> 
> 
> On 3/16/2022 8:12 PM, Frederic Weisbecker wrote:
> > Give a proper self-explanatory name to the expedited grace period
> > internal polling flag.
> > 
> > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
> > Cc: Joel Fernandes <joel@...lfernandes.org>
> > ---
> >   kernel/rcu/rcu.h      | 5 +++++
> >   kernel/rcu/tree.c     | 2 +-
> >   kernel/rcu/tree_exp.h | 9 +++++----
> >   3 files changed, 11 insertions(+), 5 deletions(-)
> > 
> > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> > index eccbdbdaa02e..8a62bb416ba4 100644
> > --- a/kernel/rcu/rcu.h
> > +++ b/kernel/rcu/rcu.h
> > @@ -30,6 +30,11 @@
> >   #define RCU_GET_STATE_USE_NORMAL	0x2
> >   #define RCU_GET_STATE_BAD_FOR_NORMAL	(RCU_GET_STATE_FROM_EXPEDITED | RCU_GET_STATE_USE_NORMAL)
> > +/*
> > + * Low-order bit definitions for polled grace-period internals.
> > + */
> > +#define RCU_EXP_SEQ_POLL_DONE 0x1
> 
> From what I understood, this flag is intended for lifecycle management
> of the ->exp_seq_poll_rq; with the flag set meaning that we need to re-poll,
> which could be used for cases, where there is long gap between 2 polls, such
> that the sequence wraps around. So, maybe we can name it as
> RCU_EXP_SEQ_POLL_EXPIRED? However, my understanding could be wrong here.

It may be confusing also because this patchset slightly extends the role of this
bit.

Before the patchset, the role is indeed to deal with wrapping.
After the patchset it deals with wrapping and the polling cycle.

I would say that before the patchset, the name could be RCU_EXP_SEQ_POLLABLE,
and after the patchset it can indeed be RCU_EXP_SEQ_POLL_EXPIRED.