Re: [PATCH v3 10/14] mm: Move lru union within struct page

[Vlastimil Babka <vbabka@suse.cz>]

On 04/18/2018 08:49 PM, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> Since the LRU is two words, this does not affect the double-word
> alignment of SLUB's freelist.
> 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  include/linux/mm_types.h | 102 +++++++++++++++++++--------------------
>  1 file changed, 51 insertions(+), 51 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 39521b8385c1..230d473f16da 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -72,6 +72,57 @@ struct hmm;
>  struct page {
>  	unsigned long flags;		/* Atomic flags, some possibly
>  					 * updated asynchronously */
> +	/*
> +	 * WARNING: bit 0 of the first word encode PageTail(). That means
> +	 * the rest users of the storage space MUST NOT use the bit to
> +	 * avoid collision and false-positive PageTail().
> +	 */
> +	union {
> +		struct list_head lru;	/* Pageout list, eg. active_list
> +					 * protected by zone_lru_lock !
> +					 * Can be used as a generic list
> +					 * by the page owner.
> +					 */
> +		struct dev_pagemap *pgmap; /* ZONE_DEVICE pages are never on an
> +					    * lru or handled by a slab
> +					    * allocator, this points to the
> +					    * hosting device page map.
> +					    */
> +		struct {		/* slub per cpu partial pages */
> +			struct page *next;	/* Next partial slab */
> +#ifdef CONFIG_64BIT
> +			int pages;	/* Nr of partial slabs left */
> +			int pobjects;	/* Approximate # of objects */
> +#else
> +			short int pages;
> +			short int pobjects;
> +#endif
> +		};
> +
> +		struct rcu_head rcu_head;	/* Used by SLAB
> +						 * when destroying via RCU
> +						 */
> +		/* Tail pages of compound page */
> +		struct {
> +			unsigned long compound_head; /* If bit zero is set */
> +
> +			/* First tail page only */
> +			unsigned char compound_dtor;
> +			unsigned char compound_order;
> +			/* two/six bytes available here */
> +		};
> +
> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
> +		struct {
> +			unsigned long __pad;	/* do not overlay pmd_huge_pte
> +						 * with compound_head to avoid
> +						 * possible bit 0 collision.
> +						 */
> +			pgtable_t pmd_huge_pte; /* protected by page->ptl */
> +		};
> +#endif
> +	};
> +
>  	union {		/* This union is three words (12/24 bytes) in size */
>  		struct {	/* Page cache and anonymous pages */
>  			/* See page-flags.h for PAGE_MAPPING_FLAGS */
> @@ -133,57 +184,6 @@ struct page {
>  	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
>  	atomic_t _refcount;
>  
> -	/*
> -	 * WARNING: bit 0 of the first word encode PageTail(). That means
> -	 * the rest users of the storage space MUST NOT use the bit to
> -	 * avoid collision and false-positive PageTail().
> -	 */
> -	union {
> -		struct list_head lru;	/* Pageout list, eg. active_list
> -					 * protected by zone_lru_lock !
> -					 * Can be used as a generic list
> -					 * by the page owner.
> -					 */
> -		struct dev_pagemap *pgmap; /* ZONE_DEVICE pages are never on an
> -					    * lru or handled by a slab
> -					    * allocator, this points to the
> -					    * hosting device page map.
> -					    */
> -		struct {		/* slub per cpu partial pages */
> -			struct page *next;	/* Next partial slab */
> -#ifdef CONFIG_64BIT
> -			int pages;	/* Nr of partial slabs left */
> -			int pobjects;	/* Approximate # of objects */
> -#else
> -			short int pages;
> -			short int pobjects;
> -#endif
> -		};
> -
> -		struct rcu_head rcu_head;	/* Used by SLAB
> -						 * when destroying via RCU
> -						 */
> -		/* Tail pages of compound page */
> -		struct {
> -			unsigned long compound_head; /* If bit zero is set */
> -
> -			/* First tail page only */
> -			unsigned char compound_dtor;
> -			unsigned char compound_order;
> -			/* two/six bytes available here */
> -		};
> -
> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
> -		struct {
> -			unsigned long __pad;	/* do not overlay pmd_huge_pte
> -						 * with compound_head to avoid
> -						 * possible bit 0 collision.
> -						 */
> -			pgtable_t pmd_huge_pte; /* protected by page->ptl */
> -		};
> -#endif
> -	};
> -
>  #ifdef CONFIG_MEMCG
>  	struct mem_cgroup *mem_cgroup;
>  #endif
>