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 <20210517150922.GU3672@suse.de>
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From:   Yang Shi <shy828301@gmail.com>
Date:   Mon, 17 May 2021 12:39:49 -0700
Message-ID: <CAHbLzkoj6Vn_jjWrn99oio1Oi+D4CHw9Z+6Wy4Squz-jCh2DKw@mail.gmail.com>
Subject: Re: [v2 PATCH 1/7] mm: memory: add orig_pmd to struct vm_fault
To:     Mel Gorman <mgorman@suse.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Zi Yan <ziy@nvidia.com>, Michal Hocko <mhocko@suse.com>,
        Huang Ying <ying.huang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>, linux-s390@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, May 17, 2021 at 8:09 AM Mel Gorman <mgorman@suse.de> wrote:
>
> On Tue, Apr 13, 2021 at 02:24:10PM -0700, Yang Shi wrote:
> > Add orig_pmd to struct vm_fault so the "orig_pmd" parameter used by huge page
> > fault could be removed, just like its PTE counterpart does.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> >
> > <SNIP>
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 25b9041f9925..9c5856f8cc81 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -547,6 +547,9 @@ struct vm_fault {
> >                                        * the 'address'
> >                                        */
> >       pte_t orig_pte;                 /* Value of PTE at the time of fault */
> > +     pmd_t orig_pmd;                 /* Value of PMD at the time of fault,
> > +                                      * used by PMD fault only.
> > +                                      */
> >
> >       struct page *cow_page;          /* Page handler may use for COW fault */
> >       struct page *page;              /* ->fault handlers should return a
>
> Could this be a union?

Do you mean orig_pte and orig_pmd, or cow_page and page? I think
orig_pte and orig_pmd could be union, I don't see that they are used
at the same time from vm_fault.

But cow_page and page can't since do_cow_fault() needs copy data from
page to cow_page.

>
> --
> Mel Gorman
> SUSE Labs