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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,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 F2592C3404D for ; Wed, 19 Feb 2020 03:10:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8F61324658 for ; Wed, 19 Feb 2020 03:10:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="xohwgk2Q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F61324658 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 06CCD6B0003; Tue, 18 Feb 2020 22:10:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 01D996B0006; Tue, 18 Feb 2020 22:10:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E74DD6B0007; Tue, 18 Feb 2020 22:10:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0019.hostedemail.com [216.40.44.19]) by kanga.kvack.org (Postfix) with ESMTP id CCA246B0003 for ; Tue, 18 Feb 2020 22:10:47 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 56CB1180AD81A for ; Wed, 19 Feb 2020 03:10:47 +0000 (UTC) X-FDA: 76505399334.19.bomb13_7b42857eda22f X-HE-Tag: bomb13_7b42857eda22f X-Filterd-Recvd-Size: 4063 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf26.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Feb 2020 03:10:46 +0000 (UTC) Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C25D02176D; Wed, 19 Feb 2020 03:10:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582081846; bh=+z7KkP//J/UyJ36xlsIoqcFUH/Jfs5y+BREf1Vh0pOQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=xohwgk2QG5tvLYMrLa5W6KYoeoixjneJ8R68r7nk/sL00PH6Wcz+epEQQXtUSH/SY dwE777Hz4Bn6KBu2rtmu5FImDWOhXEfHmk622/WQkEj14uuWbvkMxoOMJo59Ka2mcn wgYL1H+yiSctZQzbmYXGu4bWezIpNQUGBp3ZkGP8= Date: Tue, 18 Feb 2020 19:10:44 -0800 From: Eric Biggers To: Matthew Wilcox 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: <20200219031044.GA1075@sol.localdomain> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-14-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200217184613.19668-14-willy@infradead.org> 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, Feb 17, 2020 at 10:45:54AM -0800, Matthew Wilcox wrote: > diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst > index 7d4d09dd5e6d..81ab30fbe45c 100644 > --- a/Documentation/filesystems/vfs.rst > +++ b/Documentation/filesystems/vfs.rst > @@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined: > int (*readpage)(struct file *, struct page *); > int (*writepages)(struct address_space *, struct writeback_control *); > int (*set_page_dirty)(struct page *page); > + void (*readahead)(struct readahead_control *); > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > int (*write_begin)(struct file *, struct address_space *mapping, > @@ -781,12 +782,24 @@ cache in your filesystem. The following members are defined: > If defined, it should set the PageDirty flag, and the > PAGECACHE_TAG_DIRTY tag in the radix tree. > > +``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? In the code, the caller actually uses readahead_for_each() to iterate through and put+unlock the pages. That implies that ->readahead() must also use readahead_for_each() as well, in order for the iterator to be advanced correctly... Right? And the ownership of each page is transferred to the callee when the callee advances the iterator past that page. I don't see how ext4_readahead() and f2fs_readahead() can work at all, given that they don't advance the iterator. - Eric