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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CE409C433FE for ; Tue, 8 Nov 2022 02:57:20 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4N5t724l5pz3cK8 for ; Tue, 8 Nov 2022 13:57:18 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.130; helo=out30-130.freemail.mail.aliyun.com; envelope-from=jefflexu@linux.alibaba.com; receiver=) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4N5t6y28x3z3cBc for ; Tue, 8 Nov 2022 13:57:13 +1100 (AEDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R791e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0VUHLUO9_1667876225; Received: from localhost(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0VUHLUO9_1667876225) by smtp.aliyun-inc.com; Tue, 08 Nov 2022 10:57:06 +0800 From: Jingbo Xu To: dhowells@redhat.com, jlayton@kernel.org, xiang@kernel.org, chao@kernel.org, linux-cachefs@redhat.com, linux-erofs@lists.ozlabs.org Subject: [PATCH v2 0/2] fscache,cachefiles: add prepare_ondemand_read() interface Date: Tue, 8 Nov 2022 10:57:03 +0800 Message-Id: <20221108025705.14816-1-jefflexu@linux.alibaba.com> X-Mailer: git-send-email 2.19.1.6.gb485710b MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" 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, 162 insertions(+), 206 deletions(-) -- 2.19.1.6.gb485710b