From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752684AbcHLM0w (ORCPT ); Fri, 12 Aug 2016 08:26:52 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36701 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752113AbcHLM0i (ORCPT ); Fri, 12 Aug 2016 08:26:38 -0400 Date: Fri, 12 Aug 2016 21:25:37 +0900 From: Sergey Senozhatsky To: Vlastimil Babka Cc: Sergey Senozhatsky , js1304@gmail.com, Andrew Morton , Minchan Kim , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Joonsoo Kim Subject: Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Message-ID: <20160812122537.GA568@swordfish> References: <1470809784-11516-1-git-send-email-iamjoonsoo.kim@lge.com> <1470809784-11516-2-git-send-email-iamjoonsoo.kim@lge.com> <20160810081453.GB573@swordfish> <172b4c63-b519-cf1d-ed68-1f85f2caed14@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <172b4c63-b519-cf1d-ed68-1f85f2caed14@suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (08/11/16 11:41), Vlastimil Babka wrote: > 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. ah, indeed. didn't notice it. -ss