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Date:   Mon, 28 Feb 2022 05:41:10 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     torvalds@linux-foundation.org, akpm@linux-foundation.org,
        willy@infradead.org, kirill@shutemov.name, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: Export PageHeadHuge()
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On Mon, Feb 28, 2022 at 01:22:56PM +0000, David Howells wrote:
>     
> Export PageHeadHuge() - it's used by folio_test_hugetlb() and thence by
> such as folio_file_page() and folio_contains().  Matthew suggested I use
> the first of those instead of doing the same calculation manually - but
> I can't call it from a module.
> 
> Kirill suggested rearranging things to put it in a header, but that
> introduces header dependencies because of where constants are defined.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: willy@infradead.org
> Link: https://lore.kernel.org/r/163707085314.3221130.14783857863702203440.stgit@warthog.procyon.org.uk/
> 
> ---
>  mm/hugetlb.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 61895cc01d09..5768df43b05c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1854,6 +1854,7 @@ int PageHeadHuge(struct page *page_head)
>  
>  	return page_head[1].compound_dtor == HUGETLB_PAGE_DTOR;
>  }
> +EXPORT_SYMBOL(PageHeadHuge);

EXPORT_SYMBOL_GPL for anything hugepage related, please.