From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753659AbcFOQlO (ORCPT ); Wed, 15 Jun 2016 12:41:14 -0400 Received: from mail-lb0-f175.google.com ([209.85.217.175]:34638 "EHLO mail-lb0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752087AbcFOQlN convert rfc822-to-8bit (ORCPT ); Wed, 15 Jun 2016 12:41:13 -0400 From: Michal Nazarewicz To: Balbir Singh , Ganesh Mahendran Cc: linux-mm , "linux-kernel\@vger.kernel.org" , "akpm\@linux-foundation.org" , Vlastimil Babka , Joonsoo Kim , mhocko@suse.com, Minchan Kim , Anshuman Khandual Subject: Re: [PATCH v2] mm/page_alloc: remove unnecessary order check in __alloc_pages_direct_compact In-Reply-To: Organization: http://mina86.com/ References: <1465983258-3726-1-git-send-email-opensource.ganesh@gmail.com> User-Agent: Notmuch/0.19+53~g2e63a09 (http://notmuchmail.org) Emacs/25.1.50.1 (x86_64-unknown-linux-gnu) Face: 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 X-Face: -TR8(rDTHy/(xl?SfWd1|3:TTgDIatE^t'vop%*gVg[kn$t{EpK(P"VQ=~T2#ysNmJKN$"yTRLB4YQs$4{[.]Fc1)*O]3+XO^oXM>Q#b^ix,O)Zbn)q[y06$`e3?C)`CwR9y5riE=fv^X@x$y?D:XO6L&x4f-}}I4=VRNwiA^t1-ZrVK^07.Pi/57c_du'& X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 X-Hashcash: 1:20:160615:linux-kernel@vger.kernel.org::n2XzrBp3Oma6pHRN:0000000000000000000000000000000000SCO X-Hashcash: 1:20:160615:linux-mm@kvack.org::sCcsHsSRpQa1mf3M:00000000000000000000000000000000000000000000AjJ X-Hashcash: 1:20:160615:khandual@linux.vnet.ibm.com::jefXGjtTvo6ZXK/a:00000000000000000000000000000000000u+l X-Hashcash: 1:20:160615:opensource.ganesh@gmail.com::CC00Ajc26MrlZcQK:00000000000000000000000000000000001I1C X-Hashcash: 1:20:160615:vbabka@suse.cz::WZgFT1ziIauG3jA+:00026A7 X-Hashcash: 1:20:160615:mhocko@suse.com::SBz+p5a7RaCYhxWl:003jYp X-Hashcash: 1:20:160615:akpm@linux-foundation.org::rzBoiMA0LD08BqUm:0000000000000000000000000000000000003A6O X-Hashcash: 1:20:160615:bsingharora@gmail.com::Y65Zvd/ANdC9kVKx:00000000000000000000000000000000000000004jPH X-Hashcash: 1:20:160615:minchan@kernel.org::7ab0QYp0UUM7CxFQ:00000000000000000000000000000000000000000003PRM X-Hashcash: 1:20:160615:iamjoonsoo.kim@lge.com::rcrgbYxW879UnoJV:000000000000000000000000000000000000000EEHX Date: Wed, 15 Jun 2016 18:41:03 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 15 2016, Balbir Singh wrote: > On Wed, Jun 15, 2016 at 7:34 PM, Ganesh Mahendran > wrote: >> In the callee try_to_compact_pages(), the (order == 0) is checked, >> so remove check in __alloc_pages_direct_compact. >> >> Signed-off-by: Ganesh Mahendran >> --- >> v2: >> remove the check in __alloc_pages_direct_compact - Anshuman Khandual >> --- >> mm/page_alloc.c | 3 --- >> 1 file changed, 3 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index b9ea618..2f5a82a 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -3173,9 +3173,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, >> struct page *page; >> int contended_compaction; >> >> - if (!order) >> - return NULL; >> - >> current->flags |= PF_MEMALLOC; >> *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, >> mode, &contended_compaction); > > What is the benefit of this. Is an if check more expensive than > calling the function and returning from it? I don't feel strongly > about such changes, but its good to audit the overall code for reading > and performance. It’s a slow path so it probably doesn’t matter much. But I also don’t see whether this improves readability of the code. For performance, I would rather wait for gcc to compile kernel as one translation unit which will allow it to inline try_to_compact_pages and notice redundant order==0 check. -- Best regards ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ «If at first you don’t succeed, give up skydiving»