linux-kernel - Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb

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Message-ID: <1337273053.4281.50.camel@twins>
Date:	Thu, 17 May 2012 18:44:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Russell King <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-mm@...ck.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>,
	Chris Metcalf <cmetcalf@...era.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb

On Thu, 2012-05-17 at 18:33 +0200, Peter Zijlstra wrote:
> On Thu, 2012-05-17 at 18:24 +0200, Peter Zijlstra wrote:
> > On Thu, 2012-05-17 at 17:00 +0100, Catalin Marinas wrote:
> > 
> > > BTW, looking at your tlb-unify branch, does tlb_remove_table() call
> > > tlb_flush/tlb_flush_mmu before freeing the tables?  I can only see
> > > tlb_remove_page() doing this. On ARM, even UP, we need the TLB flushing
> > > after clearing the pmd and before freeing the pte page table (and
> > > ideally doing it less often than at every pte_free_tlb() call).
> > 
> > No I don't think it does, so far the only archs using the RCU stuff are
> > ppc,sparc and s390 and none of those needed that (Xen might join them
> > soon though). But I will have to look and consider this more carefully.
> > I 'lost' most of the ppc/sparc/s390 details from memory to say this with
> > any certainty.
> 
> 
> Hmm, no, thinking more that does indeed sounds strange, I'll still have
> to consider it more carefully, but I think you might have found a bug
> there.

So the RCU code can from ppc in commit
267239116987d64850ad2037d8e0f3071dc3b5ce, which has similar behaviour.
Also I suspect the mm_users < 2 test will be incorrect for ARM since
even the one user can be concurrent with your speculation engine.


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