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Date:   Wed, 14 Jun 2023 11:19:48 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrea Arcangeli <aarcange@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        James Houghton <jthoughton@google.com>,
        Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH 6/7] mm/gup: Accelerate thp gup even for "pages != NULL"
Message-ID: <ZInalCeSNmAiG2K4@x1n>
References: <20230613215346.1022773-1-peterx@redhat.com>
 <20230613215346.1022773-7-peterx@redhat.com>
 <ZInVmrJdLWxOEkeD@casper.infradead.org>
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On Wed, Jun 14, 2023 at 03:58:34PM +0100, Matthew Wilcox wrote:
> On Tue, Jun 13, 2023 at 05:53:45PM -0400, Peter Xu wrote:
> > +			if (page_increm > 1)
> > +				WARN_ON_ONCE(
> > +				    try_grab_folio(compound_head(page),
> 
> You don't need to call compound_head() here; try_grab_folio() works
> on tail pages just fine.

I did it with caution because two things I'm not sure: either
is_pci_p2pdma_page() or is_longterm_pinnable_page() inside, both calls
is_zone_device_page() on the page*.

But I just noticed try_grab_folio() is also used in gup_pte_range() where
the thp can be pte mapped, so I assume we at least need that to handle tail
page well.

Do we perhaps need the compound_head() in try_grab_folio() as a separate
patch?  Or maybe I was wrong on is_zone_device_page()?

> 
> > +						   page_increm - 1,
> > +						   foll_flags) == NULL);
> > +
> > +			for (j = 0; j < page_increm; j++) {
> > +				subpage = nth_page(page, j);
> > +				pages[i+j] = subpage;
> > +				flush_anon_page(vma, subpage, start + j * PAGE_SIZE);
> > +				flush_dcache_page(subpage);
> 
> You're better off calling flush_dcache_folio() right at the end.

Will do.

Thanks,

-- 
Peter Xu