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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 2478AC43460 for ; Sat, 17 Apr 2021 20:23:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04B5660FE8 for ; Sat, 17 Apr 2021 20:23:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237046AbhDQUX1 (ORCPT ); Sat, 17 Apr 2021 16:23:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38720 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236491AbhDQUXZ (ORCPT ); Sat, 17 Apr 2021 16:23:25 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1CCBC061574; Sat, 17 Apr 2021 13:22:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=BnSKcc0JSuohlN33+Pj8bhxKsI7DT+Owp2PFJxUm9vg=; b=OEMC9XOgR/fKU/0oPNUu/P7cCL FT4t01GafWZlc1vjwl9KSjRt1IY8zFxgga7gHLRR+WCKupSKq6t9mxOaZIZufePDNN7mCVh1kH9jR F0u0g7a9CwiXrlGEHglrLCjcUmY6riPVWU0Qfcwq6bjvHqJmgaIV9kM3woRxgGCelw9NDnFMhLDTu ddS052/dNjJg/5EC844nFoPlje4sglQZ/dDMtCOaSHxgsq/MS3GcQFiMjlzkT3lk3nRsLRtoZo+VR X2xbTp+70dqUigqbpfzkNLRorcOijpiu4WZdd3t8LIzJQrj1saQRlw3+7gG/AlVzE/uFz4w1OL3ap wbKEi5/Q==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lXrSi-00Belm-JF; Sat, 17 Apr 2021 20:22:44 +0000 Date: Sat, 17 Apr 2021 21:22:40 +0100 From: Matthew Wilcox To: Ilias Apalodimas Cc: brouer@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, mcroce@linux.microsoft.com, grygorii.strashko@ti.com, arnd@kernel.org, hch@lst.de, linux-snps-arc@lists.infradead.org, mhocko@kernel.org, mgorman@suse.de Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Message-ID: <20210417202240.GS2531743@casper.infradead.org> References: <20210416230724.2519198-1-willy@infradead.org> <20210416230724.2519198-2-willy@infradead.org> <20210417024522.GP2531743@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 17, 2021 at 09:32:06PM +0300, Ilias Apalodimas wrote: > > +static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr) > > +{ > > + page->dma_addr[0] = addr; > > + if (sizeof(dma_addr_t) > sizeof(unsigned long)) > > + page->dma_addr[1] = addr >> 16 >> 16; > > The 'error' that was reported will never trigger right? > I assume this was compiled with dma_addr_t as 32bits (so it triggered the > compilation error), but the if check will never allow this codepath to run. > If so can we add a comment explaining this, since none of us will remember why > in 6 months from now? That's right. I compiled it all three ways -- 32-bit, 64-bit dma, 32-bit long and 64-bit. The 32/64 bit case turn into: if (0) page->dma_addr[1] = addr >> 16 >> 16; which gets elided. So the only case that has to work is 64-bit dma and 32-bit long. I can replace this with upper_32_bits().