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Subject: Re: [RFC PATCH v2 1/4] mm/page_alloc: use helper functions to
 add/remove a page to/from buddy
To:     Aaron Lu <aaron.lu@intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Huang Ying <ying.huang@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Kemi Wang <kemi.wang@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Michal Hocko <mhocko@suse.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Jordan <daniel.m.jordan@oracle.com>
References: <20180320085452.24641-1-aaron.lu@intel.com>
 <20180320085452.24641-2-aaron.lu@intel.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <d9121a55-411e-37e0-2080-00b860612cc8@suse.cz>
Date:   Tue, 20 Mar 2018 12:35:46 +0100
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On 03/20/2018 09:54 AM, Aaron Lu wrote:
> There are multiple places that add/remove a page into/from buddy,
> introduce helper functions for them.
> 
> This also makes it easier to add code when a page is added/removed
> to/from buddy.
> 
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> ---
>  mm/page_alloc.c | 65 ++++++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 39 insertions(+), 26 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3db9cfb2265b..3cdf1e10d412 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -736,12 +736,41 @@ static inline void set_page_order(struct page *page, unsigned int order)
>  	__SetPageBuddy(page);
>  }
>  
> +static inline void add_to_buddy_common(struct page *page, struct zone *zone,
> +					unsigned int order, int mt)
> +{
> +	set_page_order(page, order);
> +	zone->free_area[order].nr_free++;

The 'mt' parameter seems unused here. Otherwise

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

> +}
> +
> +static inline void add_to_buddy_head(struct page *page, struct zone *zone,
> +					unsigned int order, int mt)
> +{
> +	add_to_buddy_common(page, zone, order, mt);
> +	list_add(&page->lru, &zone->free_area[order].free_list[mt]);
> +}
> +
> +static inline void add_to_buddy_tail(struct page *page, struct zone *zone,
> +					unsigned int order, int mt)
> +{
> +	add_to_buddy_common(page, zone, order, mt);
> +	list_add_tail(&page->lru, &zone->free_area[order].free_list[mt]);
> +}
> +
>  static inline void rmv_page_order(struct page *page)
>  {
>  	__ClearPageBuddy(page);
>  	set_page_private(page, 0);
>  }
>  
> +static inline void remove_from_buddy(struct page *page, struct zone *zone,
> +					unsigned int order)
> +{
> +	list_del(&page->lru);
> +	zone->free_area[order].nr_free--;
> +	rmv_page_order(page);
> +}
> +
>  /*
>   * This function checks whether a page is free && is the buddy
>   * we can do coalesce a page and its buddy if
> @@ -845,13 +874,10 @@ static inline void __free_one_page(struct page *page,
>  		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
>  		 * merge with it and move up one order.
>  		 */
> -		if (page_is_guard(buddy)) {
> +		if (page_is_guard(buddy))
>  			clear_page_guard(zone, buddy, order, migratetype);
> -		} else {
> -			list_del(&buddy->lru);
> -			zone->free_area[order].nr_free--;
> -			rmv_page_order(buddy);
> -		}
> +		else
> +			remove_from_buddy(buddy, zone, order);
>  		combined_pfn = buddy_pfn & pfn;
>  		page = page + (combined_pfn - pfn);
>  		pfn = combined_pfn;
> @@ -883,8 +909,6 @@ static inline void __free_one_page(struct page *page,
>  	}
>  
>  done_merging:
> -	set_page_order(page, order);
> -
>  	/*
>  	 * If this is not the largest possible page, check if the buddy
>  	 * of the next-highest order is free. If it is, it's possible
> @@ -901,15 +925,12 @@ static inline void __free_one_page(struct page *page,
>  		higher_buddy = higher_page + (buddy_pfn - combined_pfn);
>  		if (pfn_valid_within(buddy_pfn) &&
>  		    page_is_buddy(higher_page, higher_buddy, order + 1)) {
> -			list_add_tail(&page->lru,
> -				&zone->free_area[order].free_list[migratetype]);
> -			goto out;
> +			add_to_buddy_tail(page, zone, order, migratetype);
> +			return;
>  		}
>  	}
>  
> -	list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
> -out:
> -	zone->free_area[order].nr_free++;
> +	add_to_buddy_head(page, zone, order, migratetype);
>  }
>  
>  /*
> @@ -1731,9 +1752,7 @@ static inline void expand(struct zone *zone, struct page *page,
>  		if (set_page_guard(zone, &page[size], high, migratetype))
>  			continue;
>  
> -		list_add(&page[size].lru, &area->free_list[migratetype]);
> -		area->nr_free++;
> -		set_page_order(&page[size], high);
> +		add_to_buddy_head(&page[size], zone, high, migratetype);
>  	}
>  }
>  
> @@ -1877,9 +1896,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>  							struct page, lru);
>  		if (!page)
>  			continue;
> -		list_del(&page->lru);
> -		rmv_page_order(page);
> -		area->nr_free--;
> +		remove_from_buddy(page, zone, current_order);
>  		expand(zone, page, order, current_order, area, migratetype);
>  		set_pcppage_migratetype(page, migratetype);
>  		return page;
> @@ -2795,9 +2812,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
>  	}
>  
>  	/* Remove page from free list */
> -	list_del(&page->lru);
> -	zone->free_area[order].nr_free--;
> -	rmv_page_order(page);
> +	remove_from_buddy(page, zone, order);
>  
>  	/*
>  	 * Set the pageblock if the isolated page is at least half of a
> @@ -7886,9 +7901,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>  		pr_info("remove from free list %lx %d %lx\n",
>  			pfn, 1 << order, end_pfn);
>  #endif
> -		list_del(&page->lru);
> -		rmv_page_order(page);
> -		zone->free_area[order].nr_free--;
> +		remove_from_buddy(page, zone, order);
>  		for (i = 0; i < (1 << order); i++)
>  			SetPageReserved((page+i));
>  		pfn += (1 << order);
>