linux-kernel - Re: [PATCH] Revert "mm: rename _count, field of the struct page, to

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Message-ID: <20160616105928.GA12437@dhcp22.suse.cz>
Date:	Thu, 16 Jun 2016 12:59:28 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Vlastimil Babka <vbabka@...e.cz>,
	Hugh Dickins <hughd@...gle.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] Revert "mm: rename _count, field of the struct page, to
 _refcount"

On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote:
> Christoph Hellwig <hch@...radead.org> 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. struct page is nothing the userspace should depend
on.

-- 
Michal Hocko
SUSE Labs