linux-kernel - Re: [RFC tip/locking/lockdep v5 15/17] lockdep: Reduce the size of lock

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Date:   Fri, 23 Feb 2018 20:40:23 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andrea Parri <parri.andrea@...il.com>
Subject: Re: [RFC tip/locking/lockdep v5 15/17] lockdep: Reduce the size of
 lock_list

On Fri, Feb 23, 2018 at 12:38:43PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 22, 2018 at 03:09:02PM +0800, Boqun Feng wrote:
> > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > index a1f91f8680bd..3fce8dbf5091 100644
> > --- a/include/linux/lockdep.h
> > +++ b/include/linux/lockdep.h
> > @@ -186,11 +186,11 @@ struct lock_list {
> >  	struct list_head		entry;
> >  	struct lock_class		*class;
> >  	struct stack_trace		trace;
> > -	int				distance;
> > +	u16				distance;
> >  	/* bitmap of different dependencies from head to this */
> > -	u16				dep;
> > +	u8				dep;
> >  	/* used by BFS to record whether this is picked as a recursive read */
> > -	u16				is_rr;
> > +	bool				is_rr;
> 
> Don't use bool, use u8 if you want a single byte. sizeof(_Bool) is part
> of the architecture ABI and can be up to 4 bytes (well really anything,
> but I've not seen it bigger than 4 bytes for any sane implementation).

Got it, thanks!

Regards,
Boqun

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