linux-kernel - Re: [PATCH 08/21] mm: Preemptible mmu

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Date:	Mon, 29 Nov 2010 21:47:02 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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,
	linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Russell King <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jeff Dike <jdike@...toit.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 08/21] mm: Preemptible mmu_gather

On Mon, 2010-11-29 at 11:53 +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 26 Nov 2010 15:38:51 +0100
> Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > Make mmu_gather preemptible by using a small on stack list and use
> > an option allocation to speed things up.
> > 
> > Preemptible mmu_gather is desired in general and usable once
> > i_mmap_lock becomes a mutex. Doing it before the mutex conversion
> > saves us from having to rework the code by moving the mmu_gather
> > bits inside the i_mmap_lock.
> > 
> > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > Cc: David Miller <davem@...emloft.net>
> > Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> > Cc: Russell King <rmk@....linux.org.uk>
> > Cc: Paul Mundt <lethal@...ux-sh.org>
> > Cc: Jeff Dike <jdike@...toit.com>
> > Cc: Tony Luck <tony.luck@...el.com>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> 
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Interesting, Hmm, how about using the 1st freed pages as tlb->pages
> rathet than calling alloc_page() ? no benefits ?

We could try that, but we need to be careful there, you need to wait
till after the TLB invalidate and possibly an RCU period for the
page-directory pages (sparc/powerpc).

So doing an optimistic allocation before the TLB invalidate seems saner.

Also, see patch 20.
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