Re: [PATCH 2/2] mm/debug-pagealloc: cleanup page guard code

[Vlastimil Babka <vbabka@suse.cz>]

On 11/07/2014 08:35 AM, Joonsoo Kim wrote:
> Page guard is used by debug-pagealloc feature. Currently,
> it is open-coded, but, I think that more abstraction of it makes
> core page allocator code more readable.
>
> There is no functional difference.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

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

> ---
>   mm/page_alloc.c |   38 +++++++++++++++++++-------------------
>   1 file changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d673f64..c0dbede 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -440,18 +440,29 @@ static int __init debug_guardpage_minorder_setup(char *buf)
>   }
>   __setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
>
> -static inline void set_page_guard_flag(struct page *page)
> +static inline void set_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype)
>   {
>   	__set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +	INIT_LIST_HEAD(&page->lru);
> +	set_page_private(page, order);
> +	/* Guard pages are not available for any usage */
> +	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
>   }
>
> -static inline void clear_page_guard_flag(struct page *page)
> +static inline void clear_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype)
>   {
>   	__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +	set_page_private(page, 0);
> +	if (!is_migrate_isolate(migratetype))
> +		__mod_zone_freepage_state(zone, (1 << order), migratetype);
>   }
>   #else
> -static inline void set_page_guard_flag(struct page *page) { }
> -static inline void clear_page_guard_flag(struct page *page) { }
> +static inline void set_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype) {}
> +static inline void clear_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype) {}
>   #endif
>
>   static inline void set_page_order(struct page *page, unsigned int order)
> @@ -582,12 +593,7 @@ static inline void __free_one_page(struct page *page,
>   		 * merge with it and move up one order.
>   		 */
>   		if (page_is_guard(buddy)) {
> -			clear_page_guard_flag(buddy);
> -			set_page_private(buddy, 0);
> -			if (!is_migrate_isolate(migratetype)) {
> -				__mod_zone_freepage_state(zone, 1 << order,
> -							  migratetype);
> -			}
> +			clear_page_guard(zone, buddy, order, migratetype);
>   		} else {
>   			list_del(&buddy->lru);
>   			zone->free_area[order].nr_free--;
> @@ -862,23 +868,17 @@ static inline void expand(struct zone *zone, struct page *page,
>   		size >>= 1;
>   		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
>
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -		if (high < debug_guardpage_minorder()) {
> +		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
> +			high < debug_guardpage_minorder()) {
>   			/*
>   			 * Mark as guard pages (or page), that will allow to
>   			 * merge back to allocator when buddy will be freed.
>   			 * Corresponding page table entries will not be touched,
>   			 * pages will stay not present in virtual address space
>   			 */
> -			INIT_LIST_HEAD(&page[size].lru);
> -			set_page_guard_flag(&page[size]);
> -			set_page_private(&page[size], high);
> -			/* Guard pages are not available for any usage */
> -			__mod_zone_freepage_state(zone, -(1 << high),
> -						  migratetype);
> +			set_page_guard(zone, &page[size], high, migratetype);
>   			continue;
>   		}
> -#endif
>   		list_add(&page[size].lru, &area->free_list[migratetype]);
>   		area->nr_free++;
>   		set_page_order(&page[size], high);
>

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