linux-kernel - Re: [PATCH 09/13] mm, powerpc: Move the RCU page-table freeing into generic code

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Date:	Fri, 9 Apr 2010 13:35:32 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 09/13] mm, powerpc: Move the RCU page-table freeing
 into generic code

On Thu, Apr 08, 2010 at 09:17:46PM +0200, Peter Zijlstra wrote:
> Index: linux-2.6/include/asm-generic/tlb.h
> ===================================================================
> --- linux-2.6.orig/include/asm-generic/tlb.h
> +++ linux-2.6/include/asm-generic/tlb.h
> @@ -27,6 +27,49 @@
>    #define tlb_fast_mode(tlb) 1
>  #endif
>  
> +#ifdef HAVE_ARCH_RCU_TABLE_FREE
> +/*
> + * Semi RCU freeing of the page directories.
> + *
> + * This is needed by some architectures to implement gup_fast().

Really? I see the comment in the powerpc code, but powerpc was already
using RCU before gup_fast(), and AFAIKS it is indeed using it so that
it can handle faults by getting the linux pte with find_linux_pte ?

I would have thought this should be a well used method for handling
software TLB faults.

But anyway this looks like a nice abstraction.

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