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Date: Tue, 24 Jul 2012 17:09:11 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic
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Message-ID: <20120724140911.GA8270@otc-wbsnb-06>
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To: Andrew Morton <akpm@linux-foundation.org>
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>, Tim Chen <tim.c.chen@linux.intel.com>, Alex Shi <alex.shu@intel.com>, 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


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On Mon, Jul 23, 2012 at 04:30:20PM -0700, Andrew Morton wrote:
> On Fri, 20 Jul 2012 15:50:16 +0300
> "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
>=20
> > 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.
> >=20
> > It would be nice to test the patchset with more workloads. Especially if
> > you see performance regression with THP.
> >=20
> > Any feedback is appreciated.
>=20
> This all looks pretty sane to me.  Some detail-poking from the x86 guys
> would be nice.
>=20
> What do other architectures need to do?  Simply implement
> clear_page_nocache()?

And define ARCH_HAS_USER_NOCACHE to 1.

> 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?

Okay.

--=20
 Kirill A. Shutemov

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