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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 8FD96C433E2 for ; Fri, 11 Sep 2020 07:20:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 525F32073E for ; Fri, 11 Sep 2020 07:20:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725881AbgIKHUm (ORCPT ); Fri, 11 Sep 2020 03:20:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:40620 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725776AbgIKHUj (ORCPT ); Fri, 11 Sep 2020 03:20:39 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E782EACDF; Fri, 11 Sep 2020 07:20:51 +0000 (UTC) Date: Fri, 11 Sep 2020 09:20:35 +0200 From: Michal Hocko To: David Hildenbrand Cc: Dave Hansen , Gerald Schaefer , "akpm@linux-foundation.org" , Greg KH , Jan =?iso-8859-1?Q?H=F6ppner?= , Heiko Carstens , "linux-mm@kvack.org" , linux-api@vger.kernel.org, Dave Hansen , "linux-kernel@vger.kernel.org" Subject: Re: Ways to deprecate /sys/devices/system/memory/memoryX/phys_device ? Message-ID: <20200911072035.GC7986@dhcp22.suse.cz> References: <3E00A442-7107-48DA-8172-EED95F6E1663@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3E00A442-7107-48DA-8172-EED95F6E1663@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 10-09-20 22:31:09, David Hildenbrand wrote: > > > > Am 10.09.2020 um 22:01 schrieb Dave Hansen : > > > > On 9/10/20 3:20 AM, David Hildenbrand wrote: > >> I was just exploring how /sys/devices/system/memory/memoryX/phys_device > >> is/was used. It's one of these interfaces that most probably never > >> should have been added but now we are stuck with it. > > > > While I'm all for cleanups, what specific problems is phys_device causing? > > > > Mostly stumbling over it, understanding that it is basically unused > with new userspace for good reason, questioning its existence. > > E.g., I am working on virtio-mem support for s390x. Displaying > misleading/wrong phys_device indications isn‘t particularly helpful > - especially once there are different ways to hotplug memory for an > architecture. > > > Are you hoping that we can just remove users of memoryX/* until there > > are no more left, and this is the easiest place to start? > > At least reducing it to a minimum with clear semantics. Even with > automatic onlining there are still reasons why we need to keep the > interface for now (e.g., reloading kexec to update the kdump headers > on memory hot(un)plug). But also standby memory handling on s399x > requires it (->manual onlining). While I agree that the existing interface is far from ideal, I am not sure it makes much sense to invest energy into cleaning it up. We can have a pig with a lipstick but but this will not solve the underlying problem that we have I believe. The interface doesn't scale with the block count (especially on some platforms like ppc), it is too inflexible (single size of the block) and many others. I believe we need a completely new interface which would effectively deprecate the existing one. One could still chose to use the old interface but new usecases would use the new one ideally. I have brought that up earlier already without much follow up (http://lkml.kernel.org/r/20200619120704.GD12177@dhcp22.suse.cz) -- Michal Hocko SUSE Labs