From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D93C6C4360C for ; Fri, 4 Oct 2019 11:32:17 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 84F7E2070B for ; Fri, 4 Oct 2019 11:32:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="nwkEEfEL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 84F7E2070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 46l75C0nzkzDqcq for ; Fri, 4 Oct 2019 21:32:15 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (mailfrom) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1231::1; helo=merlin.infradead.org; envelope-from=peterz@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=infradead.org header.i=@infradead.org header.b="nwkEEfEL"; dkim-atps=neutral Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 46l72G34vzzDqDt for ; Fri, 4 Oct 2019 21:29:41 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=jWelrCDVOAXy8hN8VjR1adB6IyXBOt3/QtmJ/voDmTs=; b=nwkEEfEL12BnVaYLSfPhd2e2Ln hB4i1gugq22rSMg1LCnlbu6Qno1BBRHFOYKFvZyD3L4tBd0085H+yAZ4MYaDWZ+eP9oY3o3MNjJjq BEhzcevGCSW20rEaS/5saCafPoGFWaV5v3eJouN5tEsfE5BvsGSyxBqt1fERyo/REimJh4LSRmyaD agnFLXltPj3p7qKpQ+/CtvR16C+KLJoJbaK2jrMk+LNGNWsTUGeC9qRmcCVlFJEUgAYK8Ay+xtxiS yUMpUi4BK+2/uOCdWIDdObYgY4555aqt6UZIbyTTrJBxLdCN8KfntKpA4qSjahlZ1BSiE8ZrmsiCl lZ0ESvGw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iGLlP-0005rP-Ht; Fri, 04 Oct 2019 11:28:47 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id DE8643013A4; Fri, 4 Oct 2019 13:27:54 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7BFF0203E50D2; Fri, 4 Oct 2019 13:28:44 +0200 (CEST) Date: Fri, 4 Oct 2019 13:28:44 +0200 From: Peter Zijlstra To: Leonardo Bras Subject: Re: [PATCH v5 01/11] asm-generic/pgtable: Adds generic functions to monitor lockless pgtable walks Message-ID: <20191004112844.GC19463@hirez.programming.kicks-ass.net> References: <20191003013325.2614-1-leonardo@linux.ibm.com> <20191003013325.2614-2-leonardo@linux.ibm.com> <20191003071145.GM4536@hirez.programming.kicks-ass.net> <20191003115141.GJ4581@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Song Liu , Michal Hocko , Mahesh Salgaonkar , "Dmitry V. Levin" , Keith Busch , linux-mm@kvack.org, Paul Mackerras , Christoph Lameter , Ira Weiny , Ingo Molnar , Elena Reshetova , linux-arch@vger.kernel.org, Santosh Sivaraj , Davidlohr Bueso , "Aneesh Kumar K.V" , Jann Horn , Mike Rapoport , Jason Gunthorpe , Allison Randal , Jesper Dangaard Brouer , Andrey Ryabinin , Alexey Dobriyan , Andrea Arcangeli , Ralph Campbell , Arnd Bergmann , Bartlomiej Zolnierkiewicz , John Hubbard , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , =?iso-8859-1?B?Suly9G1l?= Glisse , Mathieu Desnoyers , kvm-ppc@vger.kernel.org, Dan Williams , Reza Arbab , Vlastimil Babka , Christian Brauner , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Thomas Gleixner , Souptick Joarder , Andrew Morton , Logan Gunthorpe , Roman Gushchin , "Kirill A. Shutemov" , Al Viro Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Oct 03, 2019 at 06:24:07PM -0300, Leonardo Bras wrote: > Hello Peter, thanks for the feedback! >=20 > On Thu, 2019-10-03 at 13:51 +0200, Peter Zijlstra wrote: > > On Thu, Oct 03, 2019 at 09:11:45AM +0200, Peter Zijlstra wrote: > > > On Wed, Oct 02, 2019 at 10:33:15PM -0300, Leonardo Bras wrote: > > > > diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pg= table.h > > > > index 818691846c90..3043ea9812d5 100644 > > > > --- a/include/asm-generic/pgtable.h > > > > +++ b/include/asm-generic/pgtable.h > > > > @@ -1171,6 +1171,64 @@ static inline bool arch_has_pfn_modify_check= (void) > > > > #endif > > > > #endif > > > > =20 > > > > +#ifndef __HAVE_ARCH_LOCKLESS_PGTBL_WALK_CONTROL > > > > +static inline unsigned long begin_lockless_pgtbl_walk(struct mm_st= ruct *mm) > > > > +{ > > > > + unsigned long irq_mask; > > > > + > > > > + if (IS_ENABLED(CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING)) > > > > + atomic_inc(&mm->lockless_pgtbl_walkers); > > >=20 > > > This will not work for file backed THP. Also, this is a fairly serious > > > contention point all on its own. > >=20 > > Kiryl says we have tmpfs-thp, this would be broken vs that, as would > > your (PowerPC) use of mm_cpumask() for that IPI. >=20 > Could you please explain it? > I mean, why this breaks tmpfs-thp? > Also, why mm_cpumask() is also broken? Because shared pages are not bound by a mm; or does it not share the thp state between mappings? > > And I still think all that wrong, you really shouldn't need to wait on > > munmap(). >=20 > That is something I need to better understand. I mean, before coming > with this patch, I thought exactly this: not serialize when on munmap.=20 >=20 > But on the way I was convinced it would not work on munmap. I need to > recall why, and if it was false to assume this, re-think the whole > solution. And once you (re)figure it out, please write it down. It is a crucial bit of the puzzle and needs to be part of the Changelogs.