linux-kernel - Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM

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Date:	Mon, 2 Nov 2015 10:10:23 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Jungseok Lee <jungseoklee85@...il.com>
cc:	catalin.marinas@....com, will.deacon@....com, tj@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	james.morse@....com, takahiro.akashi@...aro.org,
	mark.rutland@....com, barami97@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu
 area setup

On Sun, 1 Nov 2015, Jungseok Lee wrote:

> There is no room to adjust 'atom_size' now when a generic percpu area
> is used. It would be redundant to write down an architecture-specific
> setup_per_cpu_areas() in order to only change the 'atom_size'. Thus,
> this patch adds a new definition, PERCPU_ATOM_SIZE, which is PAGE_SIZE
> by default. The value could be updated if needed by architecture.

What is atom_size? Why would you want a difference allocation size here?
The percpu area is virtually mapped regardless. So you will have
contiguous addresses even without atom_size.

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