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Date: Thu, 11 Aug 2016 11:41:12 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>, js1304@...il.com Cc: Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com> Subject: Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code 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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