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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 8A2E4C677FC for ; Thu, 11 Oct 2018 17:30:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4C2672075B for ; Thu, 11 Oct 2018 17:30:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4C2672075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=deltatee.com 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 S1727877AbeJLA6k (ORCPT ); Thu, 11 Oct 2018 20:58:40 -0400 Received: from ale.deltatee.com ([207.54.116.67]:59606 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726126AbeJLA6j (ORCPT ); Thu, 11 Oct 2018 20:58:39 -0400 Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.89) (envelope-from ) id 1gAemt-0002Cu-3o; Thu, 11 Oct 2018 11:30:16 -0600 From: Logan Gunthorpe To: Christoph Hellwig Cc: Rob Herring , Albert Ou , Andrew Waterman , linux-sh@vger.kernel.org, Palmer Dabbelt , linux-kernel@vger.kernel.org, Stephen Bates , Zong Li , linux-mm@kvack.org, Olof Johansson , linux-riscv@lists.infradead.org, Michael Clark , linux-arm-kernel@lists.infradead.org References: <20181005161642.2462-1-logang@deltatee.com> <20181005161642.2462-6-logang@deltatee.com> <20181011133730.GB7276@lst.de> <8cea5ffa-5fbf-8ea2-b673-20e2d09a910d@deltatee.com> Message-ID: <8ebf1a13-ec4e-c546-641c-f8dcb1f6c44d@deltatee.com> Date: Thu, 11 Oct 2018 11:30:07 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <8cea5ffa-5fbf-8ea2-b673-20e2d09a910d@deltatee.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: linux-arm-kernel@lists.infradead.org, michaeljclark@mac.com, linux-riscv@lists.infradead.org, olof@lixom.net, linux-mm@kvack.org, zong@andestech.com, sbates@raithlin.com, linux-kernel@vger.kernel.org, palmer@sifive.com, linux-sh@vger.kernel.org, andrew@sifive.com, aou@eecs.berkeley.edu, robh@kernel.org, hch@lst.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH 5/5] RISC-V: Implement sparsemem X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-10-11 10:24 a.m., Logan Gunthorpe wrote: > On 2018-10-11 7:37 a.m., Christoph Hellwig wrote: >>> +/* >>> + * Log2 of the upper bound of the size of a struct page. Used for sizing >>> + * the vmemmap region only, does not affect actual memory footprint. >>> + * We don't use sizeof(struct page) directly since taking its size here >>> + * requires its definition to be available at this point in the inclusion >>> + * chain, and it may not be a power of 2 in the first place. >>> + */ >>> +#define STRUCT_PAGE_MAX_SHIFT 6 >> >> I know this is copied from arm64, but wouldn't this be a good time >> to move this next to the struct page defintion? >> >> Also this: >> >> arch/arm64/mm/init.c: BUILD_BUG_ON(sizeof(struct page) > (1 << STRUCT_PAGE_MAX_SHIFT)); >> >> should move to comment code (or would have to be duplicated for riscv) > > Makes sense. Where is a good place for the BUILD_BUG_ON in common code? Never mind. Seems like it's pretty trivial to do this: #define STRUCT_PAGE_MAX_SHIFT \ ilog2(roundup_pow_of_two(sizeof(struct page))) So the BUILD_BUG_ON becomes unnecessary. The comment saying it can't be done is really misleading as it wasn't actually difficult. Logan