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 842D7C7618B for ; Mon, 29 Jul 2019 08:06:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 528EB20693 for ; Mon, 29 Jul 2019 08:06:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727488AbfG2IG2 (ORCPT ); Mon, 29 Jul 2019 04:06:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58110 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726680AbfG2IG2 (ORCPT ); Mon, 29 Jul 2019 04:06:28 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 81EBAC057E9F; Mon, 29 Jul 2019 08:06:27 +0000 (UTC) Received: from [10.36.117.139] (ovpn-117-139.ams2.redhat.com [10.36.117.139]) by smtp.corp.redhat.com (Postfix) with ESMTP id C3FA919C59; Mon, 29 Jul 2019 08:06:24 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Rashmica Gupta , Oscar Salvador Cc: akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com, pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190625075227.15193-1-osalvador@suse.de> <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> <0cd2c142-66ba-5b6d-bc9d-fe68c1c65c77@redhat.com> 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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 29 Jul 2019 08:06:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> Of course, other interfaces might make sense. >> >> You can then start using these memory blocks and hinder them from >> getting onlined (as a safety net) via memory notifiers. >> >> That would at least avoid you having to call >> add_memory/remove_memory/offline_pages/device_online/modifying >> memblock >> states manually. > > I see what you're saying and that definitely sounds safer. > > We would still need to call remove_memory and add_memory from memtrace > as > just offlining memory doesn't remove it from the linear page tables > (if > it's still in the page tables then hardware can prefetch it and if > hardware tracing is using it then the box checkstops). That prefetching part is interesting (and nasty as well). If we could at least get rid of the manual onlining/offlining, I would be able to sleep better at night ;) One step at a time. > >> >> (binding the memory block devices to a driver would be nicer, but the >> infrastructure is not really there yet - we have no such drivers in >> place yet) >> >>> I don't know the mm code nor how the notifiers work very well so I >>> can't quite see how the above would work. I'm assuming memtrace >>> would >>> register a hotplug notifier and when memory is offlined from >>> userspace, >>> the callback func in memtrace would be called if the priority was >>> high >>> enough? But how do we know that the memory being offlined is >>> intended >>> for usto touch? Is there a way to offline memory from userspace not >>> using sysfs or have I missed something in the sysfs interface? >> >> The notifier would really only be used to hinder onlining as a safety >> net. User space prepares (offlines) the memory blocks and then tells >> the >> drivers which memory blocks to use. >> >>> On a second read, perhaps you are assuming that memtrace is used >>> after >>> adding new memory at runtime? If so, that is not the case. If not, >>> then >>> would you be able to clarify what I'm not seeing? >> >> The main problem I see is that you are calling >> add_memory/remove_memory() on memory your device driver doesn't own. >> It >> could reside on a DIMM if I am not mistaking (or later on >> paravirtualized memory devices like virtio-mem if I ever get to >> implement them ;) ). > > This is just for baremetal/powernv so shouldn't affect virtual memory > devices. Good to now. > >> >> How is it guaranteed that the memory you are allocating does not >> reside >> on a DIMM for example added via add_memory() by the ACPI driver? > > Good point. We don't have ACPI on powernv but currently this would try > to remove memory from any online memory node, not just the ones that > are backed by RAM. oops. Okay, so essentially no memory hotplug/unplug along with memtrace. (can we document that somewhere?). I think add_memory()/try_remove_memory() could be tolerable in these environments (as it's only boot memory). -- Thanks, David / dhildenb