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 3A95CC3B1BF for ; Sat, 15 Feb 2020 01:15:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0AF76206CC for ; Sat, 15 Feb 2020 01:15:10 +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" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727797AbgBOBPH (ORCPT ); Fri, 14 Feb 2020 20:15:07 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:51234 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727602AbgBOBPG (ORCPT ); Fri, 14 Feb 2020 20:15:06 -0500 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> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org 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.