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

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Message-Id: <20120723163020.5250e09e.akpm@linux-foundation.org>
Date:	Mon, 23 Jul 2012 16:30:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
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 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()?  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?

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