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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B23AAC433EF for ; Wed, 20 Oct 2021 10:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A73B611B0 for ; Wed, 20 Oct 2021 10:58:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230179AbhJTLAO (ORCPT ); Wed, 20 Oct 2021 07:00:14 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60601 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230106AbhJTLAN (ORCPT ); Wed, 20 Oct 2021 07:00:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634727478; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nznzQGZwFhWi7IrCsZuwpAlnduoRBn7ox7Rs/xNM+f4=; b=bdFPtxKRLIrv1rBcPp6xxNE4mX4VmDH3I7Dc1/qjaX6BU5PbYtsW0zB2j0tNL9XdB2AFcB 6XGVZX5gPC6LP4+p9YZXXBT+wtyXKQK9hBz89ThcYGZYT2UYvpIfHjKU5SxTmcIEaIFxQC ZgeGsBiTkpYOhpZxq1f8fu0TTDiFnJg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-104-d8OhdiHCN4OcfUmy5JVW4A-1; Wed, 20 Oct 2021 06:57:53 -0400 X-MC-Unique: d8OhdiHCN4OcfUmy5JVW4A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 09B5D10A8E00; Wed, 20 Oct 2021 10:57:51 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9758360D30; Wed, 20 Oct 2021 10:57:44 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <67f55d920f40bf6c49643af08fe8a5cfc97a9542.camel@kernel.org> References: <67f55d920f40bf6c49643af08fe8a5cfc97a9542.camel@kernel.org> <163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk> <163456871794.2614702.15398637170877934146.stgit@warthog.procyon.org.uk> To: Jeff Layton Cc: dhowells@redhat.com, linux-cachefs@redhat.com, Dave Wysochanski , Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org, Ilya Dryomov , ceph-devel@vger.kernel.org, Steve French , linux-cifs@vger.kernel.org, Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , v9fs-developer@lists.sourceforge.net, Trond Myklebust , Matthew Wilcox , Alexander Viro , Omar Sandoval , Linus Torvalds , linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 06/67] nfs, cifs, ceph, 9p: Disable use of fscache prior to its rewrite MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3164228.1634727463.1@warthog.procyon.org.uk> Date: Wed, 20 Oct 2021 11:57:43 +0100 Message-ID: <3164229.1634727463@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Jeff Layton wrote: > The typical way to do this would be to rebrand the existing FSCACHE > Kconfig symbols into FSCACHE_OLD and then build the new fscache > structure such that it exists in parallel with the old. That, there, is nub of the problem. You can't have parallel cachefiles drivers: There's a single userspace interface (/dev/cachefiles) and only one driver can register it. You would need to decide at compile time whether you want the converted or the unconverted network filesystems to be cached. > You'd then just drop the old infrastructure once all of the fs's are > converted to the new. You could even make them conflict with one another in > Kconfig too, so that only one could be built in during the transition period > if supporting both at runtime is too difficult. > > This approach of disabling everything is much more of an all-or-nothing > affair. It may mean less "churn" overall, but it seems less "nice" > because you have an interval of commits where fscache is non-functional. > > I'm not necessarily opposed to this approach, but I'd like to better > understand why doing it this way was preferred. I'm trying to avoid adding two parallel drivers, but change in place so that I can test parts of it as I go along. David