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

[Michal Hocko]

On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote:
> Christoph Hellwig <hch@xxxxxxxxxxxxx> 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