Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753382AbdHKNbI (ORCPT ); Fri, 11 Aug 2017 09:31:08 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50304 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753358AbdHKNbG (ORCPT ); Fri, 11 Aug 2017 09:31:06 -0400 Date: Fri, 11 Aug 2017 15:30:20 +0200 From: Peter Zijlstra To: Nadav Amit Cc: linux-mm@kvack.org, nadav.amit@gmail.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Minchan Kim , Ingo Molnar , Russell King , Tony Luck , Martin Schwidefsky , "David S. Miller" , Heiko Carstens , Yoshinori Sato , Jeff Dike , linux-arch@vger.kernel.org Subject: Re: [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem Message-ID: <20170811133020.zozuuhbw72lzolj5@hirez.programming.kicks-ass.net> References: <20170802000818.4760-1-namit@vmware.com> <20170802000818.4760-7-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170802000818.4760-7-namit@vmware.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 776 Lines: 19 On Tue, Aug 01, 2017 at 05:08:17PM -0700, Nadav Amit wrote: > void tlb_finish_mmu(struct mmu_gather *tlb, > unsigned long start, unsigned long end) > { > - arch_tlb_finish_mmu(tlb, start, end); > + /* > + * If there are parallel threads are doing PTE changes on same range > + * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB > + * flush by batching, a thread has stable TLB entry can fail to flush > + * the TLB by observing pte_none|!pte_dirty, for example so flush TLB > + * forcefully if we detect parallel PTE batching threads. > + */ > + bool force = mm_tlb_flush_nested(tlb->mm); > + > + arch_tlb_finish_mmu(tlb, start, end, force); > } I don't understand the comment nor the ordering. What guarantees we see the increment if we need to?