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Date: Mon, 21 Nov 2011 15:17:59 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
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        Rik van Riel <riel@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH 5/8] readahead: add /debug/readahead/stats
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References: <20111121091819.394895091@intel.com> <20111121093846.636765408@intel.com>
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> +static unsigned long ra_stats[RA_PATTERN_MAX][RA_ACCOUNT_MAX];

Why not make it per cpu?  That should get the overhead down, probably
even enough that it can be enabled by default.

BTW I have an older framework to make it really easy to add per
cpu stats counters to debugfs. Will repost, that would simplify
it even more.

-Andi