linux-kernel - Re: [PATCH 02/11] mm: page_vma_mapped

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Date:   Thu, 10 Jun 2021 15:45:49 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Peter Xu <peterx@...hat.com>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>,
        Wang Yugui <wangyugui@...-tech.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alistair Popple <apopple@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>, Zi Yan <ziy@...dia.com>,
        Will Deacon <will@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] mm: page_vma_mapped_walk(): settle PageHuge on
 entry

On Thu, 10 Jun 2021, Peter Xu wrote:
> On Wed, Jun 09, 2021 at 11:36:36PM -0700, Hugh Dickins wrote:
> > page_vma_mapped_walk() cleanup: get the hugetlbfs PageHuge case
> > out of the way at the start, so no need to worry about it later.
> > 
> > Signed-off-by: Hugh Dickins <hughd@...gle.com>
> > Cc: <stable@...r.kernel.org>
> > ---
> >  mm/page_vma_mapped.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> > index a6dbf714ca15..7c0504641fb8 100644
> > --- a/mm/page_vma_mapped.c
> > +++ b/mm/page_vma_mapped.c
> > @@ -153,10 +153,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> >  	if (pvmw->pmd && !pvmw->pte)
> >  		return not_found(pvmw);
> >  
> > -	if (pvmw->pte)
> > -		goto next_pte;
> > -
> >  	if (unlikely(PageHuge(page))) {
> > +		/* The only possible mapping was handled on last iteration */
> > +		if (pvmw->pte)
> > +			return not_found(pvmw);
> > +
> >  		/* when pud is not present, pte will be NULL */
> >  		pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));
> >  		if (!pvmw->pte)
> 
> Would it be even nicer to move the initial check to be after PageHuge() too?
> 
> 	if (pvmw->pmd && !pvmw->pte)
> 		return not_found(pvmw);
> 
> It looks already better, so no strong opinion.

It hadn't occurred to me to move that.  I probably wanted those two
"The only possible mapping" comments near each other.  I don't see any
particular reason to change them around now - beyond the title saying
"settle PageHuge on entry", whereas this is a few lines after entry!

Let's leave it as is.

> 
> Reviewed-by: Peter Xu <peterx@...hat.com>

Thanks,
Hugh