diff options
Diffstat (limited to 'mm/internal.h')
| -rw-r--r-- | mm/internal.h | 117 |
1 files changed, 90 insertions, 27 deletions
diff --git a/mm/internal.h b/mm/internal.h index cf16280ce132..6293468fd7b7 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -212,6 +212,67 @@ struct alloc_context { }; /* + * This function returns the order of a free page in the buddy system. In + * general, page_zone(page)->lock must be held by the caller to prevent the + * page from being allocated in parallel and returning garbage as the order. + * If a caller does not hold page_zone(page)->lock, it must guarantee that the + * page cannot be allocated or merged in parallel. Alternatively, it must + * handle invalid values gracefully, and use buddy_order_unsafe() below. + */ +static inline unsigned int buddy_order(struct page *page) +{ + /* PageBuddy() must be checked by the caller */ + return page_private(page); +} + +/* + * Like buddy_order(), but for callers who cannot afford to hold the zone lock. + * PageBuddy() should be checked first by the caller to minimize race window, + * and invalid values must be handled gracefully. + * + * READ_ONCE is used so that if the caller assigns the result into a local + * variable and e.g. tests it for valid range before using, the compiler cannot + * decide to remove the variable and inline the page_private(page) multiple + * times, potentially observing different values in the tests and the actual + * use of the result. + */ +#define buddy_order_unsafe(page) READ_ONCE(page_private(page)) + +/* + * This function checks whether a page is free && is the buddy + * we can coalesce a page and its buddy if + * (a) the buddy is not in a hole (check before calling!) && + * (b) the buddy is in the buddy system && + * (c) a page and its buddy have the same order && + * (d) a page and its buddy are in the same zone. + * + * For recording whether a page is in the buddy system, we set PageBuddy. + * Setting, clearing, and testing PageBuddy is serialized by zone->lock. + * + * For recording page's order, we use page_private(page). + */ +static inline bool page_is_buddy(struct page *page, struct page *buddy, + unsigned int order) +{ + if (!page_is_guard(buddy) && !PageBuddy(buddy)) + return false; + + if (buddy_order(buddy) != order) + return false; + + /* + * zone check is done late to avoid uselessly calculating + * zone/node ids for pages that could never merge. + */ + if (page_zone_id(page) != page_zone_id(buddy)) + return false; + + VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy); + + return true; +} + +/* * Locate the struct page for both the matching buddy in our * pair (buddy1) and the combined O(n+1) page they form (page). * @@ -234,6 +295,35 @@ __find_buddy_pfn(unsigned long page_pfn, unsigned int order) return page_pfn ^ (1 << order); } +/* + * Find the buddy of @page and validate it. + * @page: The input page + * @pfn: The pfn of the page, it saves a call to page_to_pfn() when the + * function is used in the performance-critical __free_one_page(). + * @order: The order of the page + * @buddy_pfn: The output pointer to the buddy pfn, it also saves a call to + * page_to_pfn(). + * + * The found buddy can be a non PageBuddy, out of @page's zone, or its order is + * not the same as @page. The validation is necessary before use it. + * + * Return: the found buddy page or NULL if not found. + */ +static inline struct page *find_buddy_page_pfn(struct page *page, + unsigned long pfn, unsigned int order, unsigned long *buddy_pfn) +{ + unsigned long __buddy_pfn = __find_buddy_pfn(pfn, order); + struct page *buddy; + + buddy = page + (__buddy_pfn - pfn); + if (buddy_pfn) + *buddy_pfn = __buddy_pfn; + + if (page_is_buddy(page, buddy, order)) + return buddy; + return NULL; +} + extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn, unsigned long end_pfn, struct zone *zone); @@ -337,33 +427,6 @@ int find_suitable_fallback(struct free_area *area, unsigned int order, int migratetype, bool only_stealable, bool *can_steal); /* - * This function returns the order of a free page in the buddy system. In - * general, page_zone(page)->lock must be held by the caller to prevent the - * page from being allocated in parallel and returning garbage as the order. - * If a caller does not hold page_zone(page)->lock, it must guarantee that the - * page cannot be allocated or merged in parallel. Alternatively, it must - * handle invalid values gracefully, and use buddy_order_unsafe() below. - */ -static inline unsigned int buddy_order(struct page *page) -{ - /* PageBuddy() must be checked by the caller */ - return page_private(page); -} - -/* - * Like buddy_order(), but for callers who cannot afford to hold the zone lock. - * PageBuddy() should be checked first by the caller to minimize race window, - * and invalid values must be handled gracefully. - * - * READ_ONCE is used so that if the caller assigns the result into a local - * variable and e.g. tests it for valid range before using, the compiler cannot - * decide to remove the variable and inline the page_private(page) multiple - * times, potentially observing different values in the tests and the actual - * use of the result. - */ -#define buddy_order_unsafe(page) READ_ONCE(page_private(page)) - -/* * These three helpers classifies VMAs for virtual memory accounting. */ |