From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754463AbcFPLWg (ORCPT ); Thu, 16 Jun 2016 07:22:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38917 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753919AbcFPLWc (ORCPT ); Thu, 16 Jun 2016 07:22:32 -0400 From: Vitaly Kuznetsov To: Michal Hocko Cc: Christoph Hellwig , linux-mm@kvack.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Joonsoo Kim , Andrew Morton , Stephen Rothwell , Vlastimil Babka , Hugh Dickins , Ingo Molnar Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount" References: <1466068966-24620-1-git-send-email-vkuznets@redhat.com> <20160616093235.GA14640@infradead.org> <87eg7xfmtj.fsf@vitty.brq.redhat.com> <20160616105928.GA12437@dhcp22.suse.cz> Date: Thu, 16 Jun 2016 13:22:27 +0200 In-Reply-To: <20160616105928.GA12437@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 16 Jun 2016 12:59:28 +0200") Message-ID: <87a8ilfkek.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 16 Jun 2016 11:22:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michal Hocko writes: > On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote: >> Christoph Hellwig writes: >> >> > On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote: >> >> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count, >> >> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does >> >> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While >> >> it is definitely possible to fix this particular tool I'm not sure about >> >> other tools which might be doing the same. >> >> >> >> I suggest we remember the "we don't break userspace" rule and revert for >> >> 4.7 while it's not too late. >> > >> > Err, sorry - this is not "userspace". It's crazy crap digging into >> > kernel internal structure. >> > >> > The rename was absolutely useful, so fix up your stinking pike in kdump. >> >> Ok, sure, I'll send a patch to it. I was worried about other tools out >> there which e.g. inspect /proc/vmcore. As it is something we support >> some conservatism around it is justified. > > struct page layout as some others that such a tool might depend on has > changes several times in the past so I fail to see how is it any > different this time. IMO this time the change doesn't give us any advantage, it was just a rename. > struct page is nothing the userspace should depend on. True but at least makedumpfile(8) is special and even if it's a 'crazy crap digging into ...' we could avoid breaking it for no technical reason. -- Vitaly