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Date:	Sat, 20 Sep 2014 01:26:53 -0400
From:	Tejun Heo <>
Cc:, Johannes Weiner <>
Subject: Re: [PATCH 3/3] percpu-refcount: make percpu_ref based on longs
 instead of ints

On Mon, Sep 08, 2014 at 11:12:22AM +0900, Tejun Heo wrote:
> percpu_ref is currently based on ints and the number of refs it can
> cover is (1 << 31).  This makes it impossible to use a percpu_ref to
> count memory objects or pages on 64bit machines as it may overflow.
> This forces those users to somehow aggregate the references before
> contributing to the percpu_ref which is often cumbersome and sometimes
> challenging to get the same level of performance as using the
> percpu_ref directly.
> While using ints for the percpu counters makes them pack tighter on
> 64bit machines, the possible gain from using ints instead of longs is
> extremely small compared to the overall gain from per-cpu operation.
> This patch makes percpu_ref based on longs so that it can be used to
> directly count memory objects or pages.
> Signed-off-by: Tejun Heo <>
> Cc: Kent Overstreet <>
> Cc: Johannes Weiner <>

Applied 1 and 3 to percpu/for-3.18.


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