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Date:   Wed, 14 Jun 2023 15:58:34 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Peter Xu <peterx@redhat.com>
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: <ZInVmrJdLWxOEkeD@casper.infradead.org>
References: <20230613215346.1022773-1-peterx@redhat.com>
 <20230613215346.1022773-7-peterx@redhat.com>
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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.

> +						   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.