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

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Date:	Fri, 09 Apr 2010 10:08:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nick Piggin <npiggin@...e.de>
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 Fri, 2010-04-09 at 13:35 +1000, Nick Piggin wrote:
> 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 ?

Ah, see that is my ignorance of the powerpc mmu code, I've only been
staring at this mmu_gather piece long enough to (hopefully) make it
work.

If there is indeed more to it, then yes, that needs documenting.

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