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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 3758EC3B1BF for ; Sat, 15 Feb 2020 01:15:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CC5B9206CC for ; Sat, 15 Feb 2020 01:15:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bYTz4ixA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC5B9206CC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2D6A76B0003; Fri, 14 Feb 2020 20:15:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 260236B0005; Fri, 14 Feb 2020 20:15:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 127746B0006; Fri, 14 Feb 2020 20:15:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0067.hostedemail.com [216.40.44.67]) by kanga.kvack.org (Postfix) with ESMTP id EA3E26B0003 for ; Fri, 14 Feb 2020 20:15:13 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id A72C852B4 for ; Sat, 15 Feb 2020 01:15:13 +0000 (UTC) X-FDA: 76490592906.30.scale79_2d93d8eb1712a X-HE-Tag: scale79_2d93d8eb1712a X-Filterd-Recvd-Size: 3006 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Sat, 15 Feb 2020 01:15:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=8vF3wmoykU6jc6+10TSp5NOFVxwRnMSI+FSzYO1WEQQ=; b=bYTz4ixAcXgUBn5lU/9H4Qkc8U psonlrVRSl1w2Efajn8sSvZ4fc66CBslbfJ8hYC7paJRLK+yJwFFKlpcmnCuSqQ3VgQIQc9bRKzS3 RKpTi9vip5bJenIXktMAoR2hmT8VH80rF4tgY3sf4QnBz8MWKa+ALVxAEtDMgRdz1VPOIaUeTItOS 2pxc8IX2HDPzzkM5B4sWPw6NpUySd6jYHfalkiD/26kIZxfM118k/TIVrruZyhX4bQ6tIJjKq3niB ldfXT72DOy+DLMs6ox4SNWF1RllK7qc+dkUXgtwEY31BR65L8+zEdJD+0mj8Hsxex+wOSOCKsfGso 5F0cnt9Q==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j2m2z-0006lw-H3; Sat, 15 Feb 2020 01:15:05 +0000 Date: Fri, 14 Feb 2020 17:15:05 -0800 From: Matthew Wilcox To: John Hubbard Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org Subject: Re: [PATCH v5 04/13] mm: Add readahead address space operation Message-ID: <20200215011505.GD7778@bombadil.infradead.org> References: <20200211010348.6872-1-willy@infradead.org> <20200211010348.6872-5-willy@infradead.org> <755399a8-8fdf-bfac-9f23-81579ff63ddf@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <755399a8-8fdf-bfac-9f23-81579ff63ddf@nvidia.com> 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 Thu, Feb 13, 2020 at 09:36:25PM -0800, John Hubbard wrote: > > +static inline struct page *readahead_page(struct readahead_control *rac) > > +{ > > + struct page *page; > > + > > + if (!rac->nr_pages) > > + return NULL; > > + > > + page = xa_load(&rac->mapping->i_pages, rac->start); > > > Is it worth asserting that the page was found: > > VM_BUG_ON_PAGE(!page || xa_is_value(page), page); > > ? Or is that overkill here? It shouldn't be possible since they were just added in a locked state. If it did happen, it'll be caught by the assert below -- dereferencing a NULL pointer or a shadow entry is not going to go well. > > + VM_BUG_ON_PAGE(!PageLocked(page), page); > > + rac->batch_count = hpage_nr_pages(page); > > + rac->start += rac->batch_count; > > The above was surprising, until I saw the other thread with Dave and you. > I was reviewing this patchset in order to have a chance at understanding the > follow-on patchset ("Large pages in the page cache"), and it seems like that > feature has a solid head start here. :) Right, I'll document that.