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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 F3BE1C43441 for ; Fri, 23 Nov 2018 12:52:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE71720861 for ; Fri, 23 Nov 2018 12:52:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AE71720861 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S2504407AbeKWXgG (ORCPT ); Fri, 23 Nov 2018 18:36:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55854 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403778AbeKWXgG (ORCPT ); Fri, 23 Nov 2018 18:36:06 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 117E385546; Fri, 23 Nov 2018 12:52:01 +0000 (UTC) Received: from [10.36.118.36] (unknown [10.36.118.36]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8AA3717DE5; Fri, 23 Nov 2018 12:51:58 +0000 (UTC) Subject: Re: [RFC PATCH 0/4] mm, memory_hotplug: allocate memmap from hotadded memory To: Michal Hocko Cc: Oscar Salvador , linux-mm@kvack.org, rppt@linux.vnet.ibm.com, akpm@linux-foundation.org, arunks@codeaurora.org, bhe@redhat.com, dan.j.williams@intel.com, Pavel.Tatashin@microsoft.com, Jonathan.Cameron@huawei.com, jglisse@redhat.com, linux-kernel@vger.kernel.org References: <20181116101222.16581-1-osalvador@suse.com> <2571308d-0460-e8b9-ad40-75d6b13b2d09@redhat.com> <20181123115519.2dnzscmmgv63fdub@d104.suse.de> <20181123124228.GI8625@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20181123124228.GI8625@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 23 Nov 2018 12:52:01 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23.11.18 13:42, Michal Hocko wrote: > On Fri 23-11-18 12:55:41, Oscar Salvador wrote: >> On Thu, Nov 22, 2018 at 10:21:24AM +0100, David Hildenbrand wrote: >>> 1. How are we going to present such memory to the system statistics? >>> >>> In my opinion, this vmemmap memory should >>> a) still account to total memory >>> b) show up as allocated >>> >>> So just like before. >> >> No, it does not show up under total memory and neither as allocated memory. >> This memory is not for use for anything but for creating the pagetables >> for the memmap array for the section/s. > > I haven't read through your patches yet but wanted to clarfify few > points here. > > This should essentially follow the bootmem allocated memory pattern. So > it is present and accounted to spanned pages but it is not managed. > >> It is not memory that the system can use. > > same as bootmem ;) Fair enough, just saying that it represents a change :) (but people also already complained if their VM has XGB but they don't see actual XGB as total memory e.g. due to the crash kernel size) > >> I also guess that if there is a strong opinion on this, we could create >> a counter, something like NR_VMEMMAP_PAGES, and show it under /proc/meminfo. > > Do we really have to? Isn't the number quite obvious from the size of > the hotpluged memory? At least the size of vmmaps cannot reliably calculated from "MemTotal" . But maybe based on something else. (there, it is indeed obvious) > >> >>> 2. Is this optional, in other words, can a device driver decide to not >>> to it like that? >> >> Right now, is a per arch setup. >> For example, x86_64/powerpc/arm64 will do it inconditionally. >> >> If we want to restrict this a per device-driver thing, I guess that we could >> allow to pass a flag to add_memory()->add_memory_resource(), and there >> unset MHP_MEMMAP_FROM_RANGE in case that flag is enabled. > > I believe we will need to make this opt-in. There are some usecases > which hotplug an expensive (per size) memory via hotplug and it would be > too wasteful to use it for struct pages. I haven't bothered to address > that with my previous patches because I just wanted to make the damn > thing work first. > Good point. -- Thanks, David / dhildenb