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Date:   Tue, 2 Mar 2021 13:22:49 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Zi Yan <ziy@nvidia.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [PATCH v3 01/25] mm: Introduce struct folio
Message-ID: <20210302132249.GX2723601@casper.infradead.org>
References: <20210128070404.1922318-1-willy@infradead.org>
 <20210128070404.1922318-2-willy@infradead.org>
 <68723D50-AFD1-4F25-8F10-81EC11045BE5@nvidia.com>
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On Mon, Mar 01, 2021 at 03:26:11PM -0500, Zi Yan wrote:
> > +static inline struct folio *next_folio(struct folio *folio)
> > +{
> > +	return folio + folio_nr_pages(folio);
> 
> Are you planning to make hugetlb use folio too?
> 
> If yes, this might not work if we have CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_VMEMMAP
> with a hugetlb folio > MAX_ORDER, because struct page might not be virtually contiguous.
> See the experiment I did in [1].

Actually, how about proofing this against a future change?

static inline struct folio *next_folio(struct folio *folio)
{
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
	pfn_t next_pfn = page_to_pfn(&folio->page) + folio_nr_pages(folio);
	return (struct folio *)pfn_to_page(next_pfn);
#else
	return folio + folio_nr_pages(folio);
#endif
}

(not compiled)