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=-5.7 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,URIBL_BLOCKED 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 8F224C433ED for ; Sat, 17 Apr 2021 03:20:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61AB06101E for ; Sat, 17 Apr 2021 03:20:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235582AbhDQDUZ (ORCPT ); Fri, 16 Apr 2021 23:20:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233847AbhDQDUP (ORCPT ); Fri, 16 Apr 2021 23:20:15 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E3A7C061574; Fri, 16 Apr 2021 20:19:18 -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=GyfHo5X+9TYxXDQBPsebhce873z4IO94hxWr4yFJsxk=; b=eLkRpqM9nVcIRoyRLRDTRb+BGw 8Awo1hTN6pG0fPX4ENPtHTgJ48U/u51Nl9T7MLyFIioyj8ndHPm3xgvLjM9WDUKO5myVwtcj1L/tA vxyewxTVxm2oJidWu97Sn26XMpfCR94JhZaH1KmJvz8URVQ+vtrELkUHkUpY25zznz8ZZsxrr1F4C jZFWtzr1IDbg8asen9M5hZEr8pqF5z+i2kZWHrwxjbtCtUXLIA2GHxtapiozrml/Zzh4A0tEnLKFb ZThBj+SmcItxXjZ5LILeRy9iqYUuhHuFH2RjpdGU724ns0j//tKwz/QkauIH43rk3hZw41DH66Nr6 qRM5Tlkw==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lXbUA-00AmRw-8N; Sat, 17 Apr 2021 03:19:10 +0000 Date: Sat, 17 Apr 2021 04:19:06 +0100 From: Matthew Wilcox To: Jesper Dangaard Brouer Cc: David Laight , "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" , Ilias Apalodimas , Matteo Croce , Grygorii Strashko , Arnd Bergmann , Christoph Hellwig Subject: Re: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Message-ID: <20210417031906.GQ2531743@casper.infradead.org> References: <20210411103318.GC2531743@casper.infradead.org> <20210412011532.GG2531743@casper.infradead.org> <20210414101044.19da09df@carbon> <20210414115052.GS2531743@casper.infradead.org> <20210414211322.3799afd4@carbon> <20210414213556.GY2531743@casper.infradead.org> <20210415200832.32796445@carbon> <20210416152755.GL2531743@casper.infradead.org> <20210416190823.3b3aace0@carbon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210416190823.3b3aace0@carbon> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 16, 2021 at 07:08:23PM +0200, Jesper Dangaard Brouer wrote: > On Fri, 16 Apr 2021 16:27:55 +0100 > Matthew Wilcox wrote: > > > On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote: > > > See below patch. Where I swap32 the dma address to satisfy > > > page->compound having bit zero cleared. (It is the simplest fix I could > > > come up with). > > > > I think this is slightly simpler, and as a bonus code that assumes the > > old layout won't compile. > > This is clever, I like it! When reading the code one just have to > remember 'unsigned long' size difference between 64-bit vs 32-bit. > And I assume compiler can optimize the sizeof check out then doable. I checked before/after with the replacement patch that doesn't have compiler warnings. On x86, there is zero codegen difference (objdump -dr before/after matches exactly) for both x86-32 with 32-bit dma_addr_t and x86-64. For x86-32 with 64-bit dma_addr_t, the compiler makes some different inlining decisions in page_pool_empty_ring(), page_pool_put_page() and page_pool_put_page_bulk(), but it's not clear to me that they're wrong. Function old new delta page_pool_empty_ring 387 307 -80 page_pool_put_page 604 516 -88 page_pool_put_page_bulk 690 517 -173