On 08/10/2016 10:14 AM, Sergey Senozhatsky wrote:
@@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page, size >>= 1; VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]); - if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) && - debug_guardpage_enabled() && - 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 - */ - set_page_guard(zone, &page[size], high, migratetype); + /* + * 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 + */ + if (set_page_guard(zone, &page[size], high, migratetype)) continue; - }so previously IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) could have optimized out the entire branch -- no set_page_guard() invocation and checks, right? but now we would call set_page_guard() every time?
No, there's a !CONFIG_DEBUG_PAGEALLOC version of set_page_guard() that returns false (static inline), so this whole if will be eliminated by the compiler, same as before.
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