linux-kernel - Re: [PATCH 03/12] mm/pagewalk: Skip dax pages in pagewalk

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Message-ID: <473e974b-39a1-4ee1-b321-58f6a74c0155@redhat.com>
Date: Fri, 30 May 2025 11:42:49 +0200
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org
Cc: gerald.schaefer@...ux.ibm.com, dan.j.williams@...el.com, jgg@...pe.ca,
 willy@...radead.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 zhang.lyra@...il.com, debug@...osinc.com, bjorn@...nel.org,
 balbirs@...dia.com, lorenzo.stoakes@...cle.com,
 linux-arm-kernel@...ts.infradead.org, loongarch@...ts.linux.dev,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 linux-cxl@...r.kernel.org, dri-devel@...ts.freedesktop.org, John@...ves.net
Subject: Re: [PATCH 03/12] mm/pagewalk: Skip dax pages in pagewalk

On 29.05.25 08:32, Alistair Popple wrote:
> Previously dax pages were skipped by the pagewalk code as pud_special() or
> vm_normal_page{_pmd}() would be false for DAX pages. Now that dax pages are
> refcounted normally that is no longer the case, so add explicit checks to
> skip them.

Is this really what we want, though? If these are now just "normal" 
pages, they shall be handled as being normal.

I would assume that we want to check that in the callers instead.

E.g., in get_mergeable_page() we already have a folio_is_zone_device() 
check.

> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>   include/linux/memremap.h | 11 +++++++++++
>   mm/pagewalk.c            | 12 ++++++++++--
>   2 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 4aa1519..54e8b57 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -198,6 +198,17 @@ static inline bool folio_is_fsdax(const struct folio *folio)
>   	return is_fsdax_page(&folio->page);
>   }
>   
> +static inline bool is_devdax_page(const struct page *page)
> +{
> +	return is_zone_device_page(page) &&
> +		page_pgmap(page)->type == MEMORY_DEVICE_GENERIC;
> +}
> +
> +static inline bool folio_is_devdax(const struct folio *folio)
> +{
> +	return is_devdax_page(&folio->page);
> +}

Hm, nobody uses folio_is_devdax() in this patch :)


-- 
Cheers,

David / dhildenb