linux-kernel - Re: [PATCH RFC v2 0/3] mm: Properly document tail pages for a folio

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Date:   Mon, 14 Aug 2023 16:01:08 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Matthew Wilcox <willy@...radead.org>, Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Kravetz <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Yang Shi <shy828301@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH RFC v2 0/3] mm: Properly document tail pages for a folio



On 8/14/23 12:58, Matthew Wilcox wrote:
> On Mon, Aug 14, 2023 at 02:44:08PM -0400, Peter Xu wrote:
> 
> Look, this is all still too complicated.  And you're trying to make
> something better that I'm trying to make disappear.  I'd really rather
> you spent your time worrying about making userfaultfd use folios
> than faffing with this.
> 
> How about this?
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5e74ce4a28cd..873285bb5d45 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -334,11 +334,14 @@ struct folio {
>   	/* public: */
>   			unsigned char _folio_dtor;
>   			unsigned char _folio_order;
> +			/* two bytes available here */
>   			atomic_t _entire_mapcount;
>   			atomic_t _nr_pages_mapped;
>   			atomic_t _pincount;
> +			/* no more space on 32-bt */

			                    32-bit

>   #ifdef CONFIG_64BIT
>   			unsigned int _folio_nr_pages;
> +			/* twelve bytes available on 64-bit */
>   #endif
>   	/* private: the union with struct page is transitional */
>   		};
> @@ -360,6 +363,7 @@ struct folio {
>   			unsigned long _head_2a;
>   	/* public: */
>   			struct list_head _deferred_list;
> +			/* three more words available here */
>   	/* private: the union with struct page is transitional */
>   		};
>   		struct page __page_2;