linux-kernel - Re: [PATCH]mmap: add alignment for some variables

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Message-Id: <20110329152434.d662706f.akpm@linux-foundation.org>
Date:	Tue, 29 Mar 2011 15:24:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH]mmap: add alignment for some variables

On Tue, 29 Mar 2011 08:54:14 +0800
Shaohua Li <shaohua.li@...el.com> wrote:

> -struct percpu_counter vm_committed_as;
> +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp;

Why ____cacheline_internodealigned_in_smp?  That's pretty aggressive.

afacit the main benefit from this will occur if the read-only
vm_committed_as.counters lands in the same cacheline as some
write-frequently storage.

But that's a complete mad guess and I'd prefer not to have to guess.

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