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Date: Thu, 13 Apr 2017 10:58:04 +0200 From: Laurent Dufour <ldufour@...ux.vnet.ibm.com> To: Jan Kara <jack@...e.cz> Cc: Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org, peterz@...radead.org, akpm@...ux-foundation.org, 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 13/04/2017 10:38, Jan Kara wrote: > 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? I do agree that this will take time, but systems become larger and having 200 threads hitting a lock like the mmap_sem every nanoseconds, it will increment faster (still need about 3 years)... if there are 1000 threads, less than 1 year to overflow this counter... This is not for today, I agree.
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