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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 73446C4332F for ; Wed, 16 Nov 2022 10:56:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233868AbiKPK4p (ORCPT ); Wed, 16 Nov 2022 05:56:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239039AbiKPK4X (ORCPT ); Wed, 16 Nov 2022 05:56:23 -0500 Received: from out30-56.freemail.mail.aliyun.com (out30-56.freemail.mail.aliyun.com [115.124.30.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AAE4959842; Wed, 16 Nov 2022 02:45:07 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0VUxXL9z_1668595503; Received: from localhost(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0VUxXL9z_1668595503) by smtp.aliyun-inc.com; Wed, 16 Nov 2022 18:45:05 +0800 From: Jingbo Xu To: xiang@kernel.org, chao@kernel.org, jlayton@kernel.org, linux-erofs@lists.ozlabs.org, linux-cachefs@redhat.com, dhowells@redhat.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v3 0/2] fscache,cachefiles: add prepare_ondemand_read() interface Date: Wed, 16 Nov 2022 18:45:00 +0800 Message-Id: <20221116104502.107431-1-jefflexu@linux.alibaba.com> X-Mailer: git-send-email 2.19.1.6.gb485710b MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org v3: - rebase to v6.1-rc5, while the xas_retry() checking in patch 2 has been extracted out as a separate fix [1] [1] commit 37020bbb71d9 ("erofs: fix missing xas_retry() in fscache mode") (https://github.com/torvalds/linux/commit/37020bbb71d9) v2: - patch 1: the generic routine, i.e. cachefiles_do_prepare_read() now accepts a parameter list instead of netfs_io_subrequest, and thus some debug info retrieved from netfs_io_subrequest is removed from trace_cachefiles_prep_read(). - patch 2: add xas_retry() checking in erofs_fscache_req_complete() [Rationale] =========== Fscache has been landed as a generic caching management framework in the Linux kernel for decades. It aims to manage cache data availability or fetch data if needed. Currently it's mainly used for network fses, but in principle the main caching subsystem can be used more widely. We do really like fscache framework and we believe it'd be better to reuse such framework if possible instead of duplicating other alternatives for better maintenance and testing. Therefore for our container image use cases, we applied the existing fscache to implement on-demand read for erofs in the past months. For more details, also see [1]. In short, here each erofs filesystem is composed of multiple blobs (or devices). Each blob corresponds to one fscache cookie to strictly follow on-disk format and implement the image downloading in a deterministic manner, which means it has a unique checksum and is signed by vendors. Data of each erofs inode can be scattered among multiple blobs (cookie) since erofs supports chunk-level deduplication. In this case, each erofs inode can correspond to multiple cookies, and there's a logical to physical offset mapping between the logical offset in erofs inode and the physical offset in the backing file. As described above, per-cookie netfs model can not be used here directly. Instead, we'd like to propose/decouple a simple set of raw fscache APIs, to access cache for all fses to use. We believe it's useful since it's like the relationship between raw bio and iomap, both of which are useful for local fses. fscache_read() seems a reasonable candidate and is enough for such use case. In addition, the on-demand read feature relies on .prepare_read() to reuse the hole detecting logic as much as possible. However, after fscache/netfs rework, libnetfs is preferred to access fscache, making .prepare_read() closely coupled with libnetfs, or more precisely, netfs_io_subrequest. [What We Do] ============ As we discussed previously, we propose a new interface, i,e, .prepare_ondemand_read() dedicated for the on-demand read scenarios, which is independent on netfs_io_subrequest. The netfs will still use the original .prepare_read() as usual. Jingbo Xu (2): fscache,cachefiles: add prepare_ondemand_read() callback erofs: switch to prepare_ondemand_read() in fscache mode fs/cachefiles/io.c | 75 +++++---- fs/erofs/fscache.c | 259 +++++++++++------------------- include/linux/netfs.h | 7 + include/trace/events/cachefiles.h | 27 ++-- 4 files changed, 160 insertions(+), 208 deletions(-) -- 2.19.1.6.gb485710b