From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 86C6A6B0005 for ; Thu, 16 Jun 2016 05:36:53 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id c82so24138004wme.2 for ; Thu, 16 Jun 2016 02:36:53 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v82si3573254wmv.10.2016.06.16.02.36.52 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 16 Jun 2016 02:36:52 -0700 (PDT) Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to _refcount" References: <1466068966-24620-1-git-send-email-vkuznets@redhat.com> From: Vlastimil Babka Message-ID: Date: Thu, 16 Jun 2016 11:36:47 +0200 MIME-Version: 1.0 In-Reply-To: <1466068966-24620-1-git-send-email-vkuznets@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vitaly Kuznetsov , linux-mm@kvack.org Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Joonsoo Kim , Andrew Morton , Stephen Rothwell , Hugh Dickins , Ingo Molnar On 06/16/2016 11:22 AM, 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. I don't think the rule applies to tools such as kdump and crash, or e.g. systemtap, that interact with kernel internals even though they are technically "userspace". They have to adapt to new kernel versions all the time, the internal APIs are not frozen. Otherwise we would be quite limited in evolving the kernel... So even though the change in question is not essential (field rename) and reverting wouldn't really hurt technical progress, this is not a sufficient reason, IMO. Thus, NAK. Vlastimil -- 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