linux-kernel - Re: [v2 PATCH 1/7] mm: memory: add orig_pmd to struct vm

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Date:   Tue, 18 May 2021 08:36:18 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Yang Shi <shy828301@...il.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Zi Yan <ziy@...dia.com>, Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        hca@...ux.ibm.com, gor@...ux.ibm.com, borntraeger@...ibm.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH 1/7] mm: memory: add orig_pmd to struct vm_fault

On Mon, May 17, 2021 at 12:39:49PM -0700, Yang Shi wrote:
> On Mon, May 17, 2021 at 8:09 AM Mel Gorman <mgorman@...e.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@...il.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?

orig_pte and orig_pmd given that one for PTE faults and one is for PMD
faults and it's very unlikely they would both need to be considered during
a single fault.

-- 
Mel Gorman
SUSE Labs