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 78BBDC433ED for ; Tue, 27 Apr 2021 03:30:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 00FCA613AE for ; Tue, 27 Apr 2021 03:30:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00FCA613AE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8F8866B006E; Mon, 26 Apr 2021 23:30:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8A7E16B0071; Mon, 26 Apr 2021 23:30:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 748C96B0072; Mon, 26 Apr 2021 23:30:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0003.hostedemail.com [216.40.44.3]) by kanga.kvack.org (Postfix) with ESMTP id 598336B006E for ; Mon, 26 Apr 2021 23:30:55 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 1BE94180AD837 for ; Tue, 27 Apr 2021 03:30:55 +0000 (UTC) X-FDA: 78076720470.15.6A665B1 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf08.hostedemail.com (Postfix) with ESMTP id AF43480192F1 for ; Tue, 27 Apr 2021 03:30:32 +0000 (UTC) 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 X-Stat-Signature: k565xodif5y6dxinisajwnewjkz183y3 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AF43480192F1 Received-SPF: none (arm.com>: No applicable sender policy available) receiver=imf08; identity=mailfrom; envelope-from=""; helo=foss.arm.com; client-ip=217.140.110.172 X-HE-DKIM-Result: none/none X-HE-Tag: 1619494232-182660 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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