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Date:   Fri, 20 Nov 2020 12:20:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com
Subject: Re: [RFC PATCH 2/3] mm: Introduce a new Vmemmap page-type

On 22.10.20 14:58, Oscar Salvador wrote:
> This patch introduces a new Vmemmap page-type so we can better
> picture and handle those kind of pages.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>   include/linux/mm.h         | 6 ++++++
>   include/linux/mm_types.h   | 5 +++++
>   include/linux/page-flags.h | 6 ++++++
>   3 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ef360fe70aaf..48845f054136 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3126,6 +3126,12 @@ static inline bool debug_guardpage_enabled(void) { return false; }
>   static inline bool page_is_guard(struct page *page) { return false; }
>   #endif /* CONFIG_DEBUG_PAGEALLOC */
>   
> +static __always_inline unsigned long vmemmap_nr_pages(struct page *page)
> +{
> +	struct page *head = (struct page *)page->vmemmap_head;
> +	return head->vmemmap_pages - (page - head);
> +}
> +
>   #if MAX_NUMNODES > 1
>   void __init setup_nr_node_ids(void);
>   #else
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index ae891c0c55fc..0bb8de4262c3 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -171,6 +171,11 @@ struct page {
>   			 * pmem backed DAX files are mapped.
>   			 */
>   		};
> +		struct {	/* Vmemmap pages */
> +			unsigned long vmemmap_head;
> +			unsigned long vmemmap_sections; /* Number of sections */
> +			unsigned long vmemmap_pages;    /* Number of pages */
> +		};
>   
>   		/** @rcu_head: You can use this to free a page by RCU. */
>   		struct rcu_head rcu_head;
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 4f6ba9379112..2bad207515fa 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -718,6 +718,7 @@ PAGEFLAG_FALSE(DoubleMap)
>   #define PG_kmemcg	0x00000200
>   #define PG_table	0x00000400
>   #define PG_guard	0x00000800
> +#define PG_vmemmap     0x00001000
>   
>   #define PageType(page, flag)						\
>   	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
> @@ -784,6 +785,11 @@ PAGE_TYPE_OPS(Table, table)
>    */
>   PAGE_TYPE_OPS(Guard, guard)
>   
> +/*
> + * Vmemmap pages (see include/linux/memory_hotplug.h).
> + */
> +PAGE_TYPE_OPS(Vmemmap, vmemmap)
> +
>   extern bool is_free_buddy_page(struct page *page);
>   
>   __PAGEFLAG(Isolated, isolated, PF_ANY);
> 

I guess this will no longer be strictly necessary to get it flying :)

-- 
Thanks,

David / dhildenb

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