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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 A3F04C19759 for ; Thu, 1 Aug 2019 07:18:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 808D22171F for ; Thu, 1 Aug 2019 07:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730732AbfHAHSw (ORCPT ); Thu, 1 Aug 2019 03:18:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46256 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725946AbfHAHSw (ORCPT ); Thu, 1 Aug 2019 03:18:52 -0400 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 0426BC04BD48; Thu, 1 Aug 2019 07:18:51 +0000 (UTC) Received: from [10.36.116.245] (ovpn-116-245.ams2.redhat.com [10.36.116.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6D6CC60623; Thu, 1 Aug 2019 07:18:48 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Michal Hocko , Rashmica Gupta Cc: Oscar Salvador , Andrew Morton , Dan Williams , pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2ebfbd36-11bd-9576-e373-2964c458185b@redhat.com> <20190626080249.GA30863@linux> <2750c11a-524d-b248-060c-49e6b3eb8975@redhat.com> <20190626081516.GC30863@linux> <887b902e-063d-a857-d472-f6f69d954378@redhat.com> <9143f64391d11aa0f1988e78be9de7ff56e4b30b.camel@gmail.com> <20190702074806.GA26836@linux> <20190731120859.GJ9330@dhcp22.suse.cz> <4ddee0dd719abd50350f997b8089fa26f6004c0c.camel@gmail.com> <20190801071709.GE11627@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/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190801071709.GE11627@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 [10.5.110.31]); Thu, 01 Aug 2019 07:18:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.08.19 09:17, Michal Hocko wrote: > On Thu 01-08-19 09:06:40, Rashmica Gupta wrote: >> On Wed, 2019-07-31 at 14:08 +0200, Michal Hocko wrote: >>> On Tue 02-07-19 18:52:01, Rashmica Gupta wrote: >>> [...] >>>>> 2) Why it was designed, what is the goal of the interface? >>>>> 3) When it is supposed to be used? >>>>> >>>>> >>>> There is a hardware debugging facility (htm) on some power chips. >>>> To use >>>> this you need a contiguous portion of memory for the output to be >>>> dumped >>>> to - and we obviously don't want this memory to be simultaneously >>>> used by >>>> the kernel. >>> >>> How much memory are we talking about here? Just curious. >> >> From what I've seen a couple of GB per node, so maybe 2-10GB total. > > OK, that is really a lot to keep around unused just in case the > debugging is going to be used. > > I am still not sure the current approach of (ab)using memory hotplug is > ideal. Sure there is some overlap but you shouldn't really need to > offline the required memory range at all. All you need is to isolate the > memory from any existing user and the page allocator. Have you checked > alloc_contig_range? > Rashmica mentioned somewhere in this thread that the virtual mapping must not be in place, otherwise the HW might prefetch some of this memory, leading to errors with memtrace (which checks that in HW). -- Thanks, David / dhildenb