From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E697C433E0 for ; Tue, 2 Mar 2021 09:09:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BA7876146D for ; Tue, 2 Mar 2021 09:09:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA7876146D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gentwo.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 25B6C8D00ED; Tue, 2 Mar 2021 04:09:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1E60E8D0063; Tue, 2 Mar 2021 04:09:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0873D8D00ED; Tue, 2 Mar 2021 04:09:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0072.hostedemail.com [216.40.44.72]) by kanga.kvack.org (Postfix) with ESMTP id E338A8D0063 for ; Tue, 2 Mar 2021 04:09:13 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id AFED0181AF5CC for ; Tue, 2 Mar 2021 09:09:13 +0000 (UTC) X-FDA: 77874360186.11.F3D69E5 Received: from gentwo.de (vmi485042.contaboserver.net [161.97.139.209]) by imf05.hostedemail.com (Postfix) with ESMTP id 08BADE0011E6 for ; Tue, 2 Mar 2021 09:09:11 +0000 (UTC) Received: by gentwo.de (Postfix, from userid 1001) id 576ABB00626; Tue, 2 Mar 2021 10:09:10 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by gentwo.de (Postfix) with ESMTP id 56A00B0061E; Tue, 2 Mar 2021 10:09:10 +0100 (CET) Date: Tue, 2 Mar 2021 10:09:10 +0100 (CET) From: Christoph Lameter To: Yejune Deng cc: penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] include/linux/slab.h: use for() and left shift to calculate In-Reply-To: <20210302033908.51706-1-yejune.deng@gmail.com> Message-ID: References: <20210302033908.51706-1-yejune.deng@gmail.com> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: i8hjjo7i9xm7akakkwn8sje1dmpcgnrm X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 08BADE0011E6 Received-SPF: none (gentwo.de>: No applicable sender policy available) receiver=imf05; identity=mailfrom; envelope-from=""; helo=gentwo.de; client-ip=161.97.139.209 X-HE-DKIM-Result: none/none X-HE-Tag: 1614676151-826552 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 2 Mar 2021, Yejune Deng wrote: > use for() and left shift to calculate the value that compared with size. There is a reason for the madness... The current code was written so compilers can do proper constant folding and eliminate the whole function entirely. If you want this change then please verify that all compilers currently in use with this code do proper constant folding and never generate code for the for loop.