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 D55FDC3405E for ; Wed, 19 Feb 2020 16:52:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AF7C62464E for ; Wed, 19 Feb 2020 16:52:47 +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="H1FNokl1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727006AbgBSQwn (ORCPT ); Wed, 19 Feb 2020 11:52:43 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:36130 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726450AbgBSQwn (ORCPT ); Wed, 19 Feb 2020 11:52:43 -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=cgHnf3SMrTZMA4DpDgtFfVIHiHWSF/Dqsrx7GRLBvxI=; b=H1FNokl1Ks6Q/eFXln6I/UnzU6 uNPywSHLbBZMMZub1YA6iLdFROQLpb7R/fkeHp2sx0LOh1LezwyK8b9RGHm1SZgBBgV0hcuEYRTAQ merEyI+w6w69t8v9PstDfEANDQwcW54pT4F2pguMCpy3hjaFfoP4hfJjnowwZoEaPgkKVPELazSh7 6MLj14ZI0IkhiXqV5kOdKJZhGS6aIbjkm7qAH2uiQ1ZhpJTCeJ83OSUkPpb8l4bDwSTNNn54WBzkn Xy0Vd/PJU5zw6BFXMmfy5bDA3dtZOsOmWEUwuKUFuf61CMwyRMl2Tf/PF4JJ6E7Tim/Qm4mru/2Bl SNgQBpHQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4SaX-0004DT-TU; Wed, 19 Feb 2020 16:52:41 +0000 Date: Wed, 19 Feb 2020 08:52:41 -0800 From: Matthew Wilcox To: Eric Biggers Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Subject: Re: [PATCH v6 08/19] mm: Add readahead address space operation Message-ID: <20200219165241.GR24185@bombadil.infradead.org> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-14-willy@infradead.org> <20200219031044.GA1075@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219031044.GA1075@sol.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Feb 18, 2020 at 07:10:44PM -0800, Eric Biggers wrote: > > +``readahead`` > > + Called by the VM to read pages associated with the address_space > > + object. The pages are consecutive in the page cache and are > > + locked. The implementation should decrement the page refcount > > + after starting I/O on each page. Usually the page will be > > + unlocked by the I/O completion handler. If the function does > > + not attempt I/O on some pages, the caller will decrement the page > > + refcount and unlock the pages for you. Set PageUptodate if the > > + I/O completes successfully. Setting PageError on any page will > > + be ignored; simply unlock the page if an I/O error occurs. > > + > > This is unclear about how "not attempting I/O" works and how that affects who is > responsible for putting and unlocking the pages. How does the caller know which > pages were not attempted? Can any arbitrary subset of pages be not attempted, > or just the last N pages? Changed to: ``readahead`` Called by the VM to read pages associated with the address_space object. The pages are consecutive in the page cache and are locked. The implementation should decrement the page refcount after starting I/O on each page. Usually the page will be unlocked by the I/O completion handler. If the filesystem decides to stop attempting I/O before reaching the end of the readahead window, it can simply return. The caller will decrement the page refcount and unlock the remaining pages for you. Set PageUptodate if the I/O completes successfully. Setting PageError on any page will be ignored; simply unlock the page if an I/O error occurs.