linux-kernel - Re: [PATCH 04/12] mm: Allow compound zone device pages

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Message-ID: <Zt_PbIADa4baLEBw@casper.infradead.org>
Date: Tue, 10 Sep 2024 05:47:40 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Alistair Popple <apopple@...dia.com>
Cc: dan.j.williams@...el.com, linux-mm@...ck.org, vishal.l.verma@...el.com,
	dave.jiang@...el.com, logang@...tatee.com, bhelgaas@...gle.com,
	jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com,
	will@...nel.org, mpe@...erman.id.au, npiggin@...il.com,
	dave.hansen@...ux.intel.com, ira.weiny@...el.com, djwong@...nel.org,
	tytso@....edu, linmiaohe@...wei.com, david@...hat.com,
	peterx@...hat.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, nvdimm@...ts.linux.dev,
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	linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
	jhubbard@...dia.com, hch@....de, david@...morbit.com,
	Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH 04/12] mm: Allow compound zone device pages

On Tue, Sep 10, 2024 at 02:14:29PM +1000, Alistair Popple wrote:
> @@ -337,6 +341,7 @@ struct folio {
>  	/* private: */
>  				};
>  	/* public: */
> +			struct dev_pagemap *pgmap;

Shouldn't that be indented by one more tab stop?

And for ease of reading, perhaps it should be placed either immediately
before or after 'struct list_head lru;'?

> +++ b/include/linux/mmzone.h
> @@ -1134,6 +1134,12 @@ static inline bool is_zone_device_page(const struct page *page)
>  	return page_zonenum(page) == ZONE_DEVICE;
>  }
>  
> +static inline struct dev_pagemap *page_dev_pagemap(const struct page *page)
> +{
> +	WARN_ON(!is_zone_device_page(page));
> +	return page_folio(page)->pgmap;
> +}

I haven't read to the end yet, but presumably we'll eventually want:

static inline struct dev_pagemap *folio_dev_pagemap(const struct folio *folio)
{
	WARN_ON(!folio_is_zone_device(folio))
	return folio->pgmap;
}

and since we'll want it eventually, maybe now is the time to add it,
and make page_dev_pagemap() simply call it?