linux-kernel - Re: [PATCH 2/6] locking: Introduce range reader/writer lock

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Date:   Thu, 13 Apr 2017 10:38:17 +0200
From:   Jan Kara <jack@...e.cz>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org, jack@...e.cz,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 2/6] locking: Introduce range reader/writer lock

On Thu 13-04-17 10:07:48, Laurent Dufour wrote:
> On 06/04/2017 18:50, Davidlohr Bueso wrote:
> > On Thu, 06 Apr 2017, Laurent Dufour wrote:
> > 
> >> How is 'seqnum' wrapping handled here ?
> >> I'd rather see something like time_before() here, isn't it ?
> > 
> > Its a 64bit counter, no overflows.
> 
> I should have miss something, what prevents this 64bit counter to not
> overflow ?
> At some point of time, this counter could reach ~0UL and then 0UL, which
> is breaking this check.

Count for yourself how long would it take for the counter to overflow if we
incremented it say every nanosecond?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR