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Subject: Re: [PATCH] percpu_counter : add percpu_counter_add_fast()
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>, Nick Piggin <npiggin@kernel.dk>,
        Dave Chinner <david@fromorbit.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Date: Fri, 22 Oct 2010 06:12:05 +0200
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Le jeudi 21 octobre 2010 à 17:45 -0700, Andrew Morton a écrit :

> this_cpu_add_return() isn't really needed in this application.
> 
> {
> 	this_cpu_add(*fbc->counters, amount);
> 	if (unlikely(abs(this_cpu_read(*fbc->counters)) > fbc->batch))
> 		out_of_line_stuff();
> }	
> 
> will work just fine.				

Hmm, you cannot do this on 32bit machines because "amount" is 64bit
wide.

Switching counters to s64 is not an option (makes summation racy, and
memory use bigger)