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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 8295DC433EF for ; Tue, 14 Sep 2021 13:54:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 655456112E for ; Tue, 14 Sep 2021 13:54:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233441AbhINN4N (ORCPT ); Tue, 14 Sep 2021 09:56:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49245 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233306AbhINN4F (ORCPT ); Tue, 14 Sep 2021 09:56:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631627687; 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: content-transfer-encoding:content-transfer-encoding; bh=rIzfcnXtGjc7TySfbNX1AsWwNTm/MWDBD4Ry2MXdNBs=; b=XmnkoZSOd7HX3mrH5FBowUbUGhjYheBvLGPRaiype9CkgP+i8gSaa8xwRHRqDvJ+yptqlj Veuf3SrXNDX+nNH02o0EMMtVAJgHiDhWoIDoji1RnugZERYeKpgiIXxXx0q1g4EN4NSSO6 CUHx3j/z74trKYCLdNFUCCcDQSLcp+g= 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-114-dIBVNSzYOdueWmxj2p5K1Q-1; Tue, 14 Sep 2021 09:54:46 -0400 X-MC-Unique: dIBVNSzYOdueWmxj2p5K1Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 97C6F8145EE; Tue, 14 Sep 2021 13:54:43 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0C68460583; Tue, 14 Sep 2021 13:54:36 +0000 (UTC) Subject: [RFC PATCH 0/8] fscache: Replace and remove old I/O API From: David Howells To: Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet Cc: linux-nfs@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Trond Myklebust , linux-cachefs@redhat.com, linux-cifs@vger.kernel.org, Shyam Prasad N , dhowells@redhat.com, Jeff Layton , Matthew Wilcox , Alexander Viro , Linus Torvalds , linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 14 Sep 2021 14:54:36 +0100 Message-ID: <163162767601.438332.9017034724960075707.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org Here's a set of patches that removes the old fscache I/O API by the following means: (1) A simple fallback API is added that can read or write a single page synchronously. The functions for this have "deprecated" in their names as they have to be removed at some point. (2) An implementation of this is provided in cachefiles. It creates a kiocb to use DIO to the backing file rather than calling readpage on the backing filesystem page and then snooping the page wait queue. (3) NFS is switched to use the fallback API. (4) CIFS is switched to use the fallback API also for the moment. (5) 9P is switched to using netfslib. (6) The old I/O API is removed from fscache and the page snooping implementation is removed from cachefiles. The reasons for doing this are: (A) Using a kiocb to do asynchronous DIO from/to the pages of the backing file is now a possibility that didn't exist when cachefiles was created. This is much simpler than the snooping mechanism with a proper callback path and it also requires fewer copies and less memory. (B) We have to stop using bmap() or SEEK_DATA/SEEK_HOLE to work out what blocks are present in the backing file is dangerous and can lead to data corruption if the backing filesystem can insert or remove blocks of zeros arbitrarily in order to optimise its extent list[1]. Whilst this patchset doesn't fix that yet, it does simplify the code and the fix for that can be made in a subsequent patchset. (C) In order to fix (B), the cache will need to keep track itself of what data is present. To make this easier to manage, the intention is to increase the cache block granularity to, say, 256KiB - importantly, a size that will span multiple pages - which means the single-page interface will have to go away. netfslib is designed to deal with that on behalf of a filesystem, though a filesystem could use raw cache calls instead and manage things itself. These patches can be found also on: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-iter-3 David Link: https://lore.kernel.org/r/YO17ZNOcq+9PajfQ@mit.edu [1] --- David Howells (8): fscache: Generalise the ->begin_read_operation method fscache: Implement an alternate I/O interface to replace the old API nfs: Move to using the alternate (deprecated) fscache I/O API 9p: (untested) Convert to using the netfs helper lib to do reads and caching cifs: (untested) Move to using the alternate (deprecated) fscache I/O API fscache: Remove the old I/O API fscache: Remove stats that are no longer used fscache: Update the documentation to reflect I/O API changes .../filesystems/caching/backend-api.rst | 138 +-- .../filesystems/caching/netfs-api.rst | 386 +----- fs/9p/Kconfig | 1 + fs/9p/cache.c | 137 --- fs/9p/cache.h | 98 +- fs/9p/v9fs.h | 9 + fs/9p/vfs_addr.c | 174 ++- fs/9p/vfs_file.c | 21 +- fs/cachefiles/Makefile | 1 - fs/cachefiles/interface.c | 15 - fs/cachefiles/internal.h | 38 - fs/cachefiles/io.c | 28 +- fs/cachefiles/main.c | 1 - fs/cachefiles/rdwr.c | 972 --------------- fs/cifs/file.c | 64 +- fs/cifs/fscache.c | 105 +- fs/cifs/fscache.h | 74 +- fs/fscache/cache.c | 6 - fs/fscache/cookie.c | 10 - fs/fscache/internal.h | 58 +- fs/fscache/io.c | 140 ++- fs/fscache/object.c | 2 - fs/fscache/page.c | 1066 ----------------- fs/fscache/stats.c | 73 +- fs/nfs/file.c | 14 +- fs/nfs/fscache-index.c | 26 - fs/nfs/fscache.c | 161 +-- fs/nfs/fscache.h | 84 +- fs/nfs/read.c | 25 +- fs/nfs/write.c | 7 +- include/linux/fscache-cache.h | 131 -- include/linux/fscache.h | 418 ++----- include/linux/netfs.h | 17 +- 33 files changed, 508 insertions(+), 3992 deletions(-) delete mode 100644 fs/cachefiles/rdwr.c