linux-kernel - Re: [PATCH] mm: Move nth_page from folio_page into folio

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Message-ID: <EBEF95E8-92ED-4381-A001-E7206FD0E1A7@nvidia.com>
Date: Thu, 13 Mar 2025 21:40:02 -0400
From: Zi Yan <ziy@...dia.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Christoph Hellwig <hch@....de>, Eric Biggers <ebiggers@...nel.org>
Subject: Re: [PATCH] mm: Move nth_page from folio_page into folio_next

On 13 Mar 2025, at 21:18, Herbert Xu wrote:

> On Thu, Mar 13, 2025 at 12:25:50PM +0000, Matthew Wilcox wrote:
>>
>> That isn't true.  HugeTLB can construct a folio which crosses a
>> contiguity boundary.
>
> Thanks.  So thea means we do need to use nth_page when iterating
> through a folio or a scatterlist generated from a folio.

When you know the folio is hugetlb with gigantic order. Folios
come out of buddy allocator are all within contiguity boundaries.
To be precise, the boundary here means a section boundary.

In addition, nth_page() is a trivial addition for SPARSEMEM_VMEMMAP
or FLATMEM. For SPARSEMEM && !SPARSEMEM_VMEMMAP, it needs to use
pfn for the calculation.

Best Regards,
Yan, Zi