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=-5.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 21F2CECDE32 for ; Wed, 17 Oct 2018 16:34:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D126C2154E for ; Wed, 17 Oct 2018 16:34:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D126C2154E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727506AbeJRAao (ORCPT ); Wed, 17 Oct 2018 20:30:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:49070 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727028AbeJRAao (ORCPT ); Wed, 17 Oct 2018 20:30:44 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 29A2FB046; Wed, 17 Oct 2018 16:34:13 +0000 (UTC) Date: Wed, 17 Oct 2018 18:34:11 +0200 From: Michal Hocko To: Alexander Duyck Cc: linux-mm@kvack.org, akpm@linux-foundation.org, pavel.tatashin@microsoft.com, dave.jiang@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, davem@davemloft.net, yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, vbabka@suse.cz, sparclinux@vger.kernel.org, dan.j.williams@intel.com, ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net, mingo@kernel.org, kirill.shutemov@linux.intel.com Subject: Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Message-ID: <20181017163411.GT18839@dhcp22.suse.cz> References: <20181015202456.2171.88406.stgit@localhost.localdomain> <20181015202656.2171.92963.stgit@localhost.localdomain> <20181017084744.GH18839@dhcp22.suse.cz> <9700b00f-a8a4-e318-f6a8-71fd1e7021b3@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9700b00f-a8a4-e318-f6a8-71fd1e7021b3@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 17-10-18 08:07:06, Alexander Duyck wrote: > On 10/17/2018 1:47 AM, Michal Hocko wrote: > > On Mon 15-10-18 13:26:56, Alexander Duyck wrote: [...] > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > > index bb0de406f8e7..ec6e57a0c14e 100644 > > > --- a/include/linux/mm.h > > > +++ b/include/linux/mm.h > > > @@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { } > > > * zeroing by defining this macro in . > > > */ > > > #ifndef mm_zero_struct_page > > > > Do we still need this ifdef? I guess we can wait for an arch which > > doesn't like this change and then add the override. I would rather go > > simple if possible. > > We probably don't, but as soon as I remove it somebody will probably > complain somewhere. I guess I could drop it for now and see if anybody > screams. Adding it back should be pretty straight forward since it would > only be 2 lines. Let's make it simpler please. If somebody really cares then this is trivial to add later. > > > +#if BITS_PER_LONG == 64 > > > +/* This function must be updated when the size of struct page grows above 80 > > > + * or reduces below 64. The idea that compiler optimizes out switch() > > > + * statement, and only leaves move/store instructions > > > + */ > > > +#define mm_zero_struct_page(pp) __mm_zero_struct_page(pp) > > > +static inline void __mm_zero_struct_page(struct page *page) > > > +{ > > > + unsigned long *_pp = (void *)page; > > > + > > > + /* Check that struct page is either 56, 64, 72, or 80 bytes */ > > > + BUILD_BUG_ON(sizeof(struct page) & 7); > > > + BUILD_BUG_ON(sizeof(struct page) < 56); > > > + BUILD_BUG_ON(sizeof(struct page) > 80); > > > + > > > + switch (sizeof(struct page)) { > > > + case 80: > > > + _pp[9] = 0; /* fallthrough */ > > > + case 72: > > > + _pp[8] = 0; /* fallthrough */ > > > + default: > > > + _pp[7] = 0; /* fallthrough */ > > > + case 56: > > > + _pp[6] = 0; > > > + _pp[5] = 0; > > > + _pp[4] = 0; > > > + _pp[3] = 0; > > > + _pp[2] = 0; > > > + _pp[1] = 0; > > > + _pp[0] = 0; > > > + } > > > > This just hit my eyes. I have to confess I have never seen default: to > > be not the last one in the switch. Can we have case 64 instead or does gcc > > complain? I would be surprised with the set of BUILD_BUG_ONs. > > I can probably just replace the "default:" with "case 64:". I think I have > seen other switch statements in the kernel without a default so odds are it > should be okay. Please do, there shouldn't be any need to obfuscate the code more than necessary. -- Michal Hocko SUSE Labs