linux-kernel - Re: [PATCH 5/7] mm/gup: Cleanup next

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Message-ID: <5886f78c-3ff8-4b64-9aa6-027c22e7d5fc@lucifer.local>
Date:   Sat, 17 Jun 2023 21:00:34 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        James Houghton <jthoughton@...gle.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 5/7] mm/gup: Cleanup next_page handling

On Sat, Jun 17, 2023 at 08:48:38PM +0100, Lorenzo Stoakes wrote:
> On Tue, Jun 13, 2023 at 05:53:44PM -0400, Peter Xu wrote:
> > The only path that doesn't use generic "**pages" handling is the gate vma.
> > Make it use the same path, meanwhile tune the next_page label upper to
> > cover "**pages" handling.  This prepares for THP handling for "**pages".
> >
> > Signed-off-by: Peter Xu <peterx@...hat.com>
> > ---
> >  mm/gup.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 8d59ae4554e7..a2d1b3c4b104 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1135,7 +1135,7 @@ static long __get_user_pages(struct mm_struct *mm,
> >  			if (!vma && in_gate_area(mm, start)) {
> >  				ret = get_gate_page(mm, start & PAGE_MASK,
> >  						gup_flags, &vma,
> > -						pages ? &pages[i] : NULL);
> > +						pages ? &page : NULL);
>
> Good spot... ugh that we handled this differently.
>
> >  				if (ret)
> >  					goto out;
> >  				ctx.page_mask = 0;
>
> We can drop this line now right? As the new next_page block will duplicate
> this.

OK I can see why you left this in given the last patch in the series :)
Please disregard.

>
> > @@ -1205,19 +1205,18 @@ static long __get_user_pages(struct mm_struct *mm,
> >  				ret = PTR_ERR(page);
> >  				goto out;
> >  			}
> > -
> > -			goto next_page;
>
> This is neat, we've already checked if pages != NULL so the if (pages)
> block at the new next_page label will not be run.
>
> >  		} else if (IS_ERR(page)) {
> >  			ret = PTR_ERR(page);
> >  			goto out;
> >  		}
> > +next_page:
> >  		if (pages) {
> >  			pages[i] = page;
> >  			flush_anon_page(vma, page, start);
> >  			flush_dcache_page(page);
>
> I guess there's no harm that we now flush here, though it seems to me to be
> superfluous, it's not a big deal I don't think.
>
> >  			ctx.page_mask = 0;
> >  		}
> > -next_page:
> > +
> >  		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
> >  		if (page_increm > nr_pages)
> >  			page_increm = nr_pages;
> > --
> > 2.40.1
> >
>
> Other than that, LGTM,
>
> Reviewed-by: Lorenzo Stoakes <lstoakes@...il.com>