linux-kernel - Re: [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic page

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Message-ID: <20120724140911.GA8270@otc-wbsnb-06>
Date:	Tue, 24 Jul 2012 17:09:11 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Alex Shi <alex.shu@...el.com>,
	Jan Beulich <jbeulich@...ell.com>,
	Robert Richter <robert.richter@....com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic
 page

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@...ux.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()?

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.

-- 
 Kirill A. Shutemov

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