From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754111AbcFPL2N (ORCPT ); Thu, 16 Jun 2016 07:28:13 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:34753 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323AbcFPL2I (ORCPT ); Thu, 16 Jun 2016 07:28:08 -0400 Date: Thu, 16 Jun 2016 13:28:06 +0200 From: Michal Hocko To: Vitaly Kuznetsov 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" Message-ID: <20160616112805.GI6836@dhcp22.suse.cz> 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> <87a8ilfkek.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a8ilfkek.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 16-06-16 13:22:27, Vitaly Kuznetsov wrote: > 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. Which would catch all the pending users who are not using the appropriate API. This is IMHO very useful as the sole purpose of the change is to catch _all_ users. So the reason is pretty much technicall. -- Michal Hocko SUSE Labs