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Date:   Wed, 13 Feb 2019 15:56:46 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 02/32] locking/lockdep: Introduce struct lock_usage

On Tue, Feb 12, 2019 at 09:38:42AM -0800, Linus Torvalds wrote:
> On Tue, Feb 12, 2019 at 9:14 AM Frederic Weisbecker <frederic@...nel.org> wrote:
> >
> > +static u64 lock_usage_mask(struct lock_usage *usage)
> > +{
> > +       return BIT(usage->bit);
> > +}
> 
> More insane "u64" - and it's *incorrect* too.
> 
>     #define BIT(nr)                    (1UL << (nr))
> 
> fundamentally means that "BIT()" can only work on up to "unsigned long".
> 
> So this odd use of u64 seems to be a disease. It only uses more memory
> (and more CPU) for no obvious reason.
> 
> u64 is not some "default type". It's expensive and shouldn't be used
> unless you have a *reason* for it.

Right, I'll simply move "[PATCH 03/32] locking/lockdep: Convert usage_mask to u64"
at the first position and follow up on that to justify its use.

Thanks.

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