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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 0852FC43441 for ; Wed, 10 Oct 2018 17:24:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEE7A2086E for ; Wed, 10 Oct 2018 17:24:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CEE7A2086E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727841AbeJKAsC (ORCPT ); Wed, 10 Oct 2018 20:48:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:42550 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726515AbeJKAsB (ORCPT ); Wed, 10 Oct 2018 20:48:01 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F047CB035; Wed, 10 Oct 2018 17:24:52 +0000 (UTC) Date: Wed, 10 Oct 2018 19:24:51 +0200 From: Michal Hocko To: Alexander Duyck Cc: Dan Williams , Linux MM , Andrew Morton , Linux Kernel Mailing List , linux-nvdimm , Pasha Tatashin , Dave Hansen , =?iso-8859-1?B?Suly9G1l?= Glisse , rppt@linux.vnet.ibm.com, Ingo Molnar , "Kirill A. Shutemov" , yi.z.zhang@linux.intel.com Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Message-ID: <20181010172451.GK5873@dhcp22.suse.cz> References: <20180925200551.3576.18755.stgit@localhost.localdomain> <20180925202053.3576.66039.stgit@localhost.localdomain> <20181009170051.GA40606@tiger-server> <25092df0-b7b4-d456-8409-9c004cb6e422@linux.intel.com> <20181010095838.GG5873@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 10-10-18 09:39:08, Alexander Duyck wrote: > On 10/10/2018 2:58 AM, Michal Hocko wrote: > > On Tue 09-10-18 13:26:41, Alexander Duyck wrote: > > [...] > > > I would think with that being the case we still probably need the call to > > > __SetPageReserved to set the bit with the expectation that it will not be > > > cleared for device-pages since the pages are not onlined. Removing the call > > > to __SetPageReserved would probably introduce a number of regressions as > > > there are multiple spots that use the reserved bit to determine if a page > > > can be swapped out to disk, mapped as system memory, or migrated. > > > > PageReserved is meant to tell any potential pfn walkers that might get > > to this struct page to back off and not touch it. Even though > > ZONE_DEVICE doesn't online pages in traditional sense it makes those > > pages available for further use so the page reserved bit should be > > cleared. > > So from what I can tell that isn't necessarily the case. Specifically if the > pagemap type is MEMORY_DEVICE_PRIVATE or MEMORY_DEVICE_PUBLIC both are > special cases where the memory may not be accessible to the CPU or cannot be > pinned in order to allow for eviction. Could you give me an example please? > The specific case that Dan and Yi are referring to is for the type > MEMORY_DEVICE_FS_DAX. For that type I could probably look at not setting the > reserved bit. Part of me wants to say that we should wait and clear the bit > later, but that would end up just adding time back to initialization. At > this point I would consider the change more of a follow-up optimization > rather than a fix though since this is tailoring things specifically for DAX > versus the other ZONE_DEVICE types. I thought I have already made it clear that these zone device hacks are not acceptable to the generic hotplug code. If the current reserve bit handling is not correct then give us a specific reason for that and we can start thinking about the proper fix. -- Michal Hocko SUSE Labs