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Subject: Re: [patch V3] percpu_counter: scalability works
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Shaohua Li <shaohua.li@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "cl@linux.com" <cl@linux.com>, "npiggin@kernel.dk" <npiggin@kernel.dk>
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Date: Tue, 17 May 2011 11:45:41 +0200
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Le mardi 17 mai 2011 à 11:11 +0200, Tejun Heo a écrit :

> I'm completely fine with #1.  I'm not that crazy but I don't really
> want to take #2 - that makes the whole _sum() interface almost
> pointless.  

Hi Tejun

_sum() is a bit more precise than percpu_counter_read(), but to make it
really precise, we means we have to stop concurrent activities, and we
never did in previous/current implementation.

We could add this (as Shaohua and myself tried in various patches)
later, if needed, but nowhere in kernel we currently need that.

Even /proc/meminfo doesnt call _sum(&vm_committed_as) but the lazy
percpu_counter_read_positive() function...

Reammy _sum() gives a good approximation of the counter, more precise
because of the percpu s32 folding, but no guarantee of deviation.