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Subject: Re: [PATCH 08/20] mm: Optimize fullmm TLB flushing
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 28 Jun 2012 18:38:13 +0200
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To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Linus Torvalds <torvalds@linux-foundation.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Alex Shi <alex.shi@intel.com>, "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>, Konrad Rzeszutek Wilk <konrad@darnok.org>, David Miller <davem@davemloft.net>, Russell King <rmk@arm.linux.org.uk>, Chris Metcalf <cmetcalf@tilera.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Tony Luck <tony.luck@intel.com>, Paul Mundt <lethal@linux-sh.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Ralf Baechle <ralf@linux-mips.org>, Kyle McMartin <kyle@mcmartin.ca>, James Bottomley <jejb@parisc-linux.org>, Chris Zankel <chris@zankel.net>

On Thu, 2012-06-28 at 18:20 +0200, Peter Zijlstra wrote:
> Now the switch_mm should imply the same cache+TBL flush we'd otherwise
> do, and I'd think that that would be the majority of the cost. Am I
> wrong there?=20

The advantage of doing this is that you don't need any of the batching
and possibly multiple invalidate nonsense you otherwise need. So it
might still be an over-all win, even if the switch is slightly more
expensive than a regular flush. Simply because you can avoid most (if
not all) the usual complexities.

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