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=-5.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 53512C4727C for ; Fri, 25 Sep 2020 15:00:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 05BD62311D for ; Fri, 25 Sep 2020 15:00:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601046003; bh=7IYT7UHLCDqtbyK4J+1ahnyggiL4z2CJopESfVBEERw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ZDzE4e5sx9aXL2/YSc3gDGff6KXV/ZlPMBAUojFexlLA5zz/OHVQYSE1XFJk+GnMb VF+VRX001FosSgHhwOeE7VbDawi/yxFI8IAgf2OGqnq6iwwovLWTFRJJXXd4KCFxid WsSgYKDUojDLiLImjQT67jQbRttsTBm4jfKAKUlQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729040AbgIYPAC (ORCPT ); Fri, 25 Sep 2020 11:00:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:42652 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728038AbgIYPAB (ORCPT ); Fri, 25 Sep 2020 11:00:01 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8E85420715; Fri, 25 Sep 2020 15:00:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601046001; bh=7IYT7UHLCDqtbyK4J+1ahnyggiL4z2CJopESfVBEERw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MrxJym8UxSkYTz/SVZc3aIPcsYOQYGu3Y5h6n1HgY+aSIvwcZgx1cwXV9ccKxstNb ZX5LjGHCsHOkZrk1hK7g1CMBJvf6tp08Y0yOA0ZTf4y5m36LUrxb9xrMUk5hBZBmKL GS7QH4CEza3i1iqOEMvj5sX++vJSWYqkCgAUFGI0= Date: Fri, 25 Sep 2020 17:00:15 +0200 From: Greg KH To: David Hildenbrand Cc: Gerald Schaefer , Michal Hocko , "akpm@linux-foundation.org" , 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: <20200925150015.GB3149196@kroah.com> References: <21852ccb-bd06-9281-7c8e-485ec02f2883@redhat.com> <20200922155611.379373f7@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Fri, Sep 25, 2020 at 04:49:28PM +0200, David Hildenbrand wrote: > >> There were once RFC patches to make use of it in ACPI, but it could be > >> solved using different interfaces [1]. > >> > >> > >> While I'd love to rip it out completely, I think it would break old > >> lsmem/chmem completely - and I assume that's not acceptable. I was > >> wondering what would be considered safe to do now/in the future: > >> > >> 1. Make it always return 0 (just as if "sclp.rzm" would be set to 0 on > >> s390x). This will make old lsmem/chmem behave differently after > >> switching to a new kernel, like if sclp.rzm would not be set by HW - > >> AFAIU, it will assume all memory is in a single memory increment. Do we > >> care? > > > > No, at least not until that kernel change would be backported to some > > old distribution level where we still use lsmem/chmem from s390-tools. > > Given that this is just some clean-up w/o any functional benefit, and > > hopefully w/o any negative impact, I think we can safely assume that no > > distributor will do that "just for fun". > > > > Even if there would be good reasons for backports, then I guess we also > > have good reasons for backporting / switching to the util-linux version > > of lsmem / chmem for such distribution levels. Alternatively, adjust the > > s390-tools lsmem / chmem there. > > > > But I would rather "rip it out completely" than just return 0. You'd > > need some lsmem / chmem changes anyway, at least in case this would > > ever be backported. > > Thanks for your input Gerald. > > So unless people would be running shiny new kernels on older > distributions it shouldn't be a problem (and I don't think we care too > much about something like that). I don't expect something like that to > get backported - there is absolutely no reason to do so IMHO. We do care about this, Andrew used to have an old Fedora 9 box or something like that, that he tourtured many of us with bug reports when we broke it :) So watch out, people keep old userspace around for much longer than you can possibly imagine because they don't like having their use-cases in userspace change, and we have made the guarantee to them that they _CAN_ trust us to not break things in userspace. It's a slow age-out, but watch out, you might have to revert things... good luck! greg k-h