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=-21.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 60819C4332F for ; Tue, 14 Sep 2021 15:49:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3DB7061212 for ; Tue, 14 Sep 2021 15:49:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235221AbhINPut (ORCPT ); Tue, 14 Sep 2021 11:50:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:43170 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235139AbhINPud (ORCPT ); Tue, 14 Sep 2021 11:50:33 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id F325D61183; Tue, 14 Sep 2021 15:49:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631634556; bh=x0wkFlR2yBgpOaQuEdr6Zq9jmODvyrdKeAmZpTWbcT0=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ajz757X0EqTjlFmBo1b2pN3UYzxhWZ0LSA5AE1BntSGzn5Ph0csrcHkpKL4NEokHJ ebG365BQDozlYjcym5lJP0GBFpNmljoYKD2rqYIzWcTQgHzZkEoeKDtmu55uN07zhq nu044qBJhD5akaeAFg19wyXuc4AO9lgXpCp1kqARn3nXXga7nKxCw0WueMjxgs9qQL c65BnTQsetg3frZwlOxgp40YCU8orREHBY2bybmLawoQ/nkKr61+IhFeBDDYdr6VjD PYAPgOau91ZgvUULY8IHTRYh6qLQUEwS9pH00FKyW90I6x9+vu0KF77C9WN8dRQBbE VQ+yUZhIDxlFQ== Message-ID: Subject: Re: [RFC PATCH 0/8] fscache: Replace and remove old I/O API From: Jeff Layton To: David Howells , 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 , Matthew Wilcox , Alexander Viro , Linus Torvalds , linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 14 Sep 2021 11:49:13 -0400 In-Reply-To: <163162767601.438332.9017034724960075707.stgit@warthog.procyon.org.uk> References: <163162767601.438332.9017034724960075707.stgit@warthog.procyon.org.uk> Content-Type: text/plain; charset="ISO-8859-15" User-Agent: Evolution 3.40.4 (3.40.4-1.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org On Tue, 2021-09-14 at 14:54 +0100, David Howells wrote: > 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 > > Love the diffstat. I looked over the set and didn't see any problems with it. I also ran a quick test with ceph+fscache and didn't run into any issues, but that's not too surprising since this patchset doesn't really change the codepaths that it uses. Reviewed-by: Jeff Layton