From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f200.google.com (mail-it1-f200.google.com [209.85.166.200]) by kanga.kvack.org (Postfix) with ESMTP id 5452D6B0003 for ; Thu, 11 Oct 2018 13:30:23 -0400 (EDT) Received: by mail-it1-f200.google.com with SMTP id z136-v6so10554342itc.5 for ; Thu, 11 Oct 2018 10:30:23 -0700 (PDT) Received: from ale.deltatee.com (ale.deltatee.com. [207.54.116.67]) by mx.google.com with ESMTPS id z196-v6si15515619itc.129.2018.10.11.10.30.22 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 11 Oct 2018 10:30:22 -0700 (PDT) From: Logan Gunthorpe 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 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 Subject: Re: [PATCH 5/5] RISC-V: Implement sparsemem Sender: owner-linux-mm@kvack.org List-ID: 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 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