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Date:   Wed, 25 Aug 2021 20:15:42 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Joao Martins <joao.m.martins@oracle.com>
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Subject: Re: [PATCH v3 13/14] mm/gup: grab head page refcount once for group
 of subpages
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References: <20210714193542.21857-1-joao.m.martins@oracle.com>
 <20210714193542.21857-14-joao.m.martins@oracle.com>
 <CAPcyv4i_BbQn6WkgeNq5kLeQcMu=w4GBdrBZ=YbuYnGC5-Dbiw@mail.gmail.com>
 <861f03ee-f8c8-cc89-3fc2-884c062fea11@oracle.com>
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On Wed, Aug 25, 2021 at 08:10:39PM +0100, Joao Martins wrote:
> @@ -2273,8 +2273,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>                 refs = record_subpages(page, addr, next, pages + *nr);
> 
>                 SetPageReferenced(head);
> -               pinned_head = try_grab_compound_head(head, refs, flags);
> -               if (unlikely(!pinned_head)) {
> +               if (unlikely(!try_grab_compound_head(head, refs, flags))) {
>                         if (PageCompound(head))

BTW, you can just check PageHead(head).  We know it can't be PageTail ...