From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 08/20] mm: Optimize fullmm TLB flushing
Date: Wed, 27 Jun 2012 15:26:18 -0700
Message-ID: <CA+55aFwZoVK76ue7tFveV0XZpPUmoCVXJx8550OxPm+XKCSSZA@mail.gmail.com>
References: <20120627211540.459910855@chello.nl> <20120627212831.137126018@chello.nl>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, 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>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Russell King <rmk@arm.linux.org.uk>, Catalin Marinas <catalin.marinas@arm.com>, 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>, Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
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On Wed, Jun 27, 2012 at 2:15 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> This originated from s390 which does something similar and would allow
> s390 to use the generic TLB flushing code.
>
> The idea is to flush the mm wide cache and tlb a priory and not bother
> with multiple flushes if the batching isn't large enough.
>
> This can be safely done since there cannot be any concurrency on this
> mm, its either after the process died (exit) or in the middle of
> execve where the thread switched to the new mm.

I think we actually *used* to do the final TLB flush from within the
context of the process that died. That doesn't seem to ever be the
case any more, but it does worry me a bit. Maybe a

   VM_BUG_ON(current->active_mm == mm);

or something for the fullmm case?

              Linus

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