linux-kernel - Re: [patch 02/41] cpu alloc: The allocator

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Message-ID: <Pine.LNX.4.64.0805292219220.12107@schroedinger.engr.sgi.com>
Date:	Thu, 29 May 2008 22:20:45 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	akpm@...ux-foundation.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>
Subject: Re: [patch 02/41] cpu alloc: The allocator

On Fri, 30 May 2008, Eric Dumazet wrote:

> > +static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]);
> >   
> area[] is not guaranteed to be aligned on anything but 4 bytes.
> 
> If someone then needs to call cpu_alloc(8, GFP_KERNEL, 8), it might get an non
> aligned result.
> 
> Either you should add an __attribute__((__aligned__(PAGE_SIZE))),
> or take into account the real address of area[] in cpu_alloc() to avoid waste
> of up to PAGE_SIZE bytes
> per cpu.

I think cacheline aligning should be sufficient. People should not 
allocate large page aligned objects here.
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