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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 205EAC433EF for ; Mon, 10 Jan 2022 08:31:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B622D6B009F; Mon, 10 Jan 2022 03:31:12 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B127C6B00A1; Mon, 10 Jan 2022 03:31:12 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A29306B00A2; Mon, 10 Jan 2022 03:31:12 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0041.hostedemail.com [216.40.44.41]) by kanga.kvack.org (Postfix) with ESMTP id 947566B009F for ; Mon, 10 Jan 2022 03:31:12 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 5B2C78248D52 for ; Mon, 10 Jan 2022 08:31:12 +0000 (UTC) X-FDA: 79013707584.28.285C6B0 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf22.hostedemail.com (Postfix) with ESMTP id 073D8C0017 for ; Mon, 10 Jan 2022 08:31:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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=e79RBh3RTVWPj6rYkP4UHRg/Ov+OQkUWfvKe2DbQ7YY=; b=CHAML+e1cyUBVcOWaNpXlSAVu6 m4CWrK994Ga2b7HmYQGIuOCsX/gMCU4BQ0MX/keA4/DlLTAIs0zWWuh4IIiKS8k0bORvkCWuk9Cpk r3Lgo0KcN6dE/iTCYL/FWatH2wyTZSR6zhKNThUZykrh8Yeb3WRPgrE+hbKl2zUDt4Hr9+3laJm54 M7TALUBT2B7k3HvXoDbE+ovLejixjK3P6lVZM/bJ9ZO6/YKjsbUXjQJNAAZ7HJN9G6gf3Af/5mh/o Mt1CqlEVZqQRxDbFN9ZxigMVpjTXCcayPuv+/yoh2MjRt+mju6jIknmhHniYtFPMhDBWMqOYj9O63 9+iZhHbQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1n6q58-009sr0-VD; Mon, 10 Jan 2022 08:31:10 +0000 Date: Mon, 10 Jan 2022 00:31:10 -0800 From: Christoph Hellwig To: "Matthew Wilcox (Oracle)" Cc: linux-mm@kvack.org, John Hubbard , Christoph Hellwig , William Kucharski , linux-kernel@vger.kernel.org, Jason Gunthorpe Subject: Re: [PATCH v2 08/28] gup: Handle page split race more efficiently Message-ID: References: <20220110042406.499429-1-willy@infradead.org> <20220110042406.499429-9-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220110042406.499429-9-willy@infradead.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: 073D8C0017 X-Stat-Signature: ia4ktza35yfm98iz51z7o8fhoaqcyaec Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=CHAML+e1; dmarc=none; spf=none (imf22.hostedemail.com: domain of BATV+996bc53df2b455107366+6714+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+996bc53df2b455107366+6714+infradead.org+hch@bombadil.srs.infradead.org X-Rspamd-Server: rspam02 X-HE-Tag: 1641803471-940186 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 Mon, Jan 10, 2022 at 04:23:46AM +0000, Matthew Wilcox (Oracle) wrote: > If we hit the page split race, the current code returns NULL which will > presumably trigger a retry under the mmap_lock. This isn't necessary; > we can just retry the compound_head() lookup. This is a very minor > optimisation of an unlikely path, but conceptually it matches (eg) > the page cache RCU-protected lookup. > > Signed-off-by: Matthew Wilcox (Oracle) Looks good, Reviewed-by: Christoph Hellwig