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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 10738C433B4 for ; Tue, 27 Apr 2021 03:30:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E308A613AA for ; Tue, 27 Apr 2021 03:30:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234625AbhD0Dbj (ORCPT ); Mon, 26 Apr 2021 23:31:39 -0400 Received: from foss.arm.com ([217.140.110.172]:43400 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234573AbhD0Dbg (ORCPT ); Mon, 26 Apr 2021 23:31:36 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 13B34D6E; Mon, 26 Apr 2021 20:30:54 -0700 (PDT) Received: from [10.163.75.249] (unknown [10.163.75.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A4F383F694; Mon, 26 Apr 2021 20:30:52 -0700 (PDT) From: Anshuman Khandual Subject: Re: [PATCH 4/6] mm: Make compound_head const-preserving To: "Matthew Wilcox (Oracle)" , linux-mm@kvack.org Cc: Andrew Morton , linux-kernel@vger.kernel.org References: <20210416231531.2521383-1-willy@infradead.org> <20210416231531.2521383-5-willy@infradead.org> Message-ID: <8c1f9169-5da5-0f1b-14cd-942f54b30ff9@arm.com> Date: Tue, 27 Apr 2021 09:01:44 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210416231531.2521383-5-willy@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/17/21 4:45 AM, Matthew Wilcox (Oracle) wrote: > If you pass a const pointer to compound_head(), you get a const pointer > back; if you pass a mutable pointer, you get a mutable pointer back. > Also remove an unnecessary forward definition of struct page; we're about > to dereference page->compound_head, so it must already have been defined. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > include/linux/page-flags.h | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 04a34c08e0a6..d8e26243db25 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -177,17 +177,17 @@ enum pageflags { > > #ifndef __GENERATING_BOUNDS_H > > -struct page; /* forward declaration */ > - > -static inline struct page *compound_head(struct page *page) > +static inline unsigned long _compound_head(const struct page *page) > { > unsigned long head = READ_ONCE(page->compound_head); > > if (unlikely(head & 1)) > - return (struct page *) (head - 1); > - return page; > + return head - 1; > + return (unsigned long)page; > } > > +#define compound_head(page) ((typeof(page))_compound_head(page)) > + > static __always_inline int PageTail(struct page *page) > { > return READ_ONCE(page->compound_head) & 1; > Reviewed-by: Anshuman Khandual