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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 329A9C433E0 for ; Thu, 14 Jan 2021 16:20:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF05D23B40 for ; Thu, 14 Jan 2021 16:20:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726287AbhANQUk (ORCPT ); Thu, 14 Jan 2021 11:20:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60706 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726212AbhANQUk (ORCPT ); Thu, 14 Jan 2021 11:20:40 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F3F13C061575; Thu, 14 Jan 2021 08:19:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=L957m6SCsm4YfRvwt1RQwkHpsqdoGDsxSLN6pjGCXjg=; b=SwgoX4biWiRfNIkgGKBzF1hThh fgohm23xOlFZxJhSLZKiwJXvlpOT7mQ1aERIfxlbDnMSz8cAhA501/6QBLnf5vxFq+Kvg8w7lNzGu lKsu5VUh30ZpNT1bDp4PgQQDOAF2zDky3QBOcd8dN/XGAqJ/p2C2tMdWALZA6gQ+xCzpv+dn065rk 2TTrQt7lGJCVnnHfj+gY6z8VUTG1gzIwprxJtAF5iFkyufA4tU7Q2Fuvhh6wXdjjz4/2sT9ZCH6eX Aa9Hq52wo/tTnFG/QpwZVj0ONsXxVxsjndY/W8xQ7Zm0pIhz05bcYui4M6gozuphqFgWnJ9k7MeB2 tBm+E3uQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1l05LN-007mRF-WF; Thu, 14 Jan 2021 16:19:41 +0000 Date: Thu, 14 Jan 2021 16:19:29 +0000 From: Matthew Wilcox To: David Howells Cc: linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com, jlayton@redhat.com, dwysocha@redhat.com, Dominique Martinet , Steve French , Trond Myklebust , Anna Schumaker , Christoph Hellwig , dchinner@redhat.com, Linus Torvalds , v9fs-developer@lists.sourceforge.net, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Redesigning and modernising fscache Message-ID: <20210114161929.GQ35215@casper.infradead.org> References: <2758811.1610621106@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2758811.1610621106@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org On Thu, Jan 14, 2021 at 10:45:06AM +0000, David Howells wrote: > However, there've been some objections to the approach I've taken to > implementing this. The way I've done it is to disable the use of fscache by > the five network filesystems that use it, remove much of the old code, put in > the reimplementation, then cut the filesystems over. I.e. rip-and-replace. > It leaves unported filesystems unable to use it - but three of the five are > done (afs, ceph, nfs), and I've supplied partially-done patches for the other > two (9p, cifs). > > It's been suggested that it's too hard to review this way and that either I > should go for a gradual phasing in or build the new one in parallel. The > first is difficult because I want to change how almost everything in there > works - but the parts are tied together; the second is difficult because there > are areas that would *have* to overlap (the UAPI device file, the cache > storage, the cache size limits and at least some state for managing these), so > there would have to be interaction between the two variants. One refinement > of the latter would be to make the two implementations mutually exclusive: you > can build one or the other, but not both. My reservation with "build fscache2" is that it's going to take some time to do, and I really want rid of ->readpages as soon as possible. What I'd like to see is netfs_readahead() existing as soon as possible, built on top of the current core. Then filesystems can implement netfs_read_request_ops one by one, and they become insulated from the transition.