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 E3645C43441 for ; Fri, 23 Nov 2018 13:17:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80BBC20863 for ; Fri, 23 Nov 2018 13:17:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 80BBC20863 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 S2504526AbeKXABo (ORCPT ); Fri, 23 Nov 2018 19:01:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46180 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394867AbeKXABo (ORCPT ); Fri, 23 Nov 2018 19:01:44 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A030C308330B; Fri, 23 Nov 2018 13:17:34 +0000 (UTC) Received: from [10.36.118.36] (unknown [10.36.118.36]) by smtp.corp.redhat.com (Postfix) with ESMTP id 34BFD5DE01; Fri, 23 Nov 2018 13:17:30 +0000 (UTC) Subject: Re: [PATCH v1] mm/memory_hotplug: drop "online" parameter from add_memory_resource() To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Andrew Morton , Dan Williams , Oscar Salvador , Pavel Tatashin , Joonsoo Kim , Arun KS , Mathieu Malaterre , Stephen Rothwell References: <20181123123740.27652-1-david@redhat.com> <20181123125400.GL8625@dhcp22.suse.cz> <20181123130546.GN8625@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: <20181123130546.GN8625@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 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 23 Nov 2018 13:17:35 +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 14:05, Michal Hocko wrote: > On Fri 23-11-18 13:58:16, David Hildenbrand wrote: >> On 23.11.18 13:54, Michal Hocko wrote: >>> On Fri 23-11-18 13:37:40, David Hildenbrand wrote: >>>> User space should always be in charge of how to online memory and >>>> if memory should be onlined automatically in the kernel. Let's drop the >>>> parameter to overwrite this - XEN passes memhp_auto_online, just like >>>> add_memory(), so we can directly use that instead internally. >>> >>> Heh, I wanted to get rid of memhp_auto_online so much and now we have it >>> in the core memory_hotplug. Not a win on my side I would say :/ >> >> That is actually a good point: Can we remove memhp_auto_online or is it >> already some sort of kernel ABI? >> >> (as it is exported via /sys/devices/system/memory/auto_online_blocks) > > I have tried and there was a pushback [1]. That led to a rework of the > sysfs semantic of onlining btw. The biggest objection against removing was > that the userspace might be too slow to online memory and memmaps could > eat the available memory and trigger OOM. That is why I've started > working on the self hosted memmpas but failed to finish it. Fortunatelly > Oscar is brave enough to continue in that work. Yes I saw that work :) . I wonder if it is really an issue or can we worked around. At least for paravirtualized devices (a.k.a. balloon devices) - even without the memmaps rework. E.g. only add a new memory block in case the old one was onlined. And we get that information via register_memory_notifier(). So we would always only have one memory block "pending to be onlined". That's at least my plan for virtio-mem (add one block at a time). The problem is if some external entity triggers memory hotplug of actual devices you cannot simply control. Like adding a bunch of ACPI DIMMs in one shot without userspace being able to keep up. But the memmaps thingy still is very valuable when wanting to add memory in an environment where we are already low on memory. > > [1] http://lkml.kernel.org/r/20170227092817.23571-1-mhocko@kernel.org > -- Thanks, David / dhildenb