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Date: Mon, 23 Jul 2012 16:30:20 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, Andi Kleen <ak@linux.intel.com>,
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        Jan Beulich <jbeulich@novell.com>,
        Robert Richter <robert.richter@amd.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Mel Gorman <mgorman@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic
 page
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On Fri, 20 Jul 2012 15:50:16 +0300
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:

> Clearing a 2MB huge page will typically blow away several levels of CPU
> caches.  To avoid this only cache clear the 4K area around the fault
> address and use a cache avoiding clears for the rest of the 2MB area.
> 
> It would be nice to test the patchset with more workloads. Especially if
> you see performance regression with THP.
> 
> Any feedback is appreciated.

This all looks pretty sane to me.  Some detail-poking from the x86 guys
would be nice.

What do other architectures need to do?  Simply implement
clear_page_nocache()?  I believe that powerpc is one, not sure about
others.  Please update the changelogs to let arch maintainers know
what they should do and cc those people on future versions?