From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-f199.google.com (mail-yw0-f199.google.com [209.85.161.199]) by kanga.kvack.org (Postfix) with ESMTP id 4868A6B025F for ; Thu, 16 Jun 2016 07:22:33 -0400 (EDT) Received: by mail-yw0-f199.google.com with SMTP id v78so43537692ywa.0 for ; Thu, 16 Jun 2016 04:22:33 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 5si26053263qgo.94.2016.06.16.04.22.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Jun 2016 04:22:32 -0700 (PDT) From: Vitaly Kuznetsov 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> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org