Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751828AbdGEQFC (ORCPT ); Wed, 5 Jul 2017 12:05:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:54112 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750896AbdGEQFB (ORCPT ); Wed, 5 Jul 2017 12:05:01 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E427E22C86 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: <20170705121807.GF4941@worktop> References: <20170705121807.GF4941@worktop> From: Andy Lutomirski Date: Wed, 5 Jul 2017 09:04:39 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID To: Peter Zijlstra Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , Borislav Petkov , Linus Torvalds , Andrew Morton , Mel Gorman , "linux-mm@kvack.org" , Nadav Amit , Rik van Riel , Dave Hansen , Arjan van de Ven Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 828 Lines: 19 On Wed, Jul 5, 2017 at 5:18 AM, Peter Zijlstra wrote: > On Thu, Jun 29, 2017 at 08:53:22AM -0700, Andy Lutomirski wrote: >> @@ -104,18 +140,20 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, >> >> /* Resume remote flushes and then read tlb_gen. */ >> cpumask_set_cpu(cpu, mm_cpumask(next)); > > Barriers should have a comment... what is being ordered here against > what? How's this comment? /* * Resume remote flushes and then read tlb_gen. We need to do * it in this order: any inc_mm_tlb_gen() caller that writes a * larger tlb_gen than we read here must see our cpu set in * mm_cpumask() so that it will know to flush us. The barrier * here synchronizes with inc_mm_tlb_gen(). */