Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967451Ab2EQQ7v (ORCPT ); Thu, 17 May 2012 12:59:51 -0400 Received: from casper.infradead.org ([85.118.1.10]:42224 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965490Ab2EQQ7s convert rfc822-to-8bit (ORCPT ); Thu, 17 May 2012 12:59:48 -0400 Message-ID: <1337273959.4281.62.camel@twins> Subject: Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb From: Peter Zijlstra To: Catalin Marinas Cc: Russell King , Paul Mundt , Andrea Arcangeli , Thomas Gleixner , Rik van Riel , Ingo Molnar , "akpm@linux-foundation.org" , Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , Benjamin Herrenschmidt , David Miller , Hugh Dickins , Mel Gorman , Nick Piggin , Chris Metcalf , Martin Schwidefsky Date: Thu, 17 May 2012 18:59:19 +0200 In-Reply-To: <1337273053.4281.50.camel@twins> References: <20110302175928.022902359@chello.nl> <20110302180259.109909335@chello.nl> <20120517030551.GA11623@linux-sh.org> <20120517093022.GA14666@arm.com> <20120517095124.GN23420@flint.arm.linux.org.uk> <1337254086.4281.26.camel@twins> <20120517160012.GB18593@arm.com> <1337271884.4281.46.camel@twins> <1337272396.4281.48.camel@twins> <1337273053.4281.50.camel@twins> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1761 Lines: 41 On Thu, 2012-05-17 at 18:44 +0200, Peter Zijlstra wrote: > > 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. > > Right, last mail, I promise, I've confused myself enough already! :-) OK, so ppc/sparc are special (forgot all about s390) I think by the time they are done with unmap_page_range() their hardware hash-tables are empty and nobody but software page-table walkers will still access the linux page tables. So when we do free_pgtables() to clean up the actual page-tables. Power/Sparc need to RCU free this to allow concurrent software page-table walkers like gup_fast. Thus I don't think they need to tlb flush again because their hardware doesn't actually walk the link page-tables, it walks hash-tables, which by this time are empty. Now if x86/Xen were to use this, it would indeed also need to TLB flush when freeing the page-tables, since its hardware walkers do indeed traverse these pages and we need to sync against them. So my first patch in the tlb-unify tree is actually buggy. Humm,. what to do adding a tlb flush in there might slow down ppc/sparc unnecessarily.. dave/ben? I guess we need more knobs :-( Now its quite possible I've utterly confused myself and everybody reading, apologies for that, I shall rest and purge all from memory and start over before commenting more.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/