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 1159AC43334 for ; Fri, 8 Jul 2022 06:07:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237158AbiGHGHx (ORCPT ); Fri, 8 Jul 2022 02:07:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236685AbiGHGHw (ORCPT ); Fri, 8 Jul 2022 02:07:52 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 960F51277B for ; Thu, 7 Jul 2022 23:07:51 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 39C9B1FEDD for ; Fri, 8 Jul 2022 06:07:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1657260470; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=vAAiSc5Qtd17mBL0FCh6zlLTn9KYpdSGbj6AmibLu/s=; b=OMi3n+NZA7hK9pNVpUuVIS+piEdY1FegwfC1D3qNN60L0AFe0y8gq5gmSgsbgXwM/InyDX v0K31ZDEB/LcyDnjbSLU2YFDE7KISGEKDeoPx2ABgALP4DcPmMV4CezIHQh1DD2St1rrGY gGhCQrhx3iYx9epw4Q1p6Gezuas4uGo= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 8089413A80 for ; Fri, 8 Jul 2022 06:07:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id NteaErXJx2KUcgAAMHmgww (envelope-from ) for ; Fri, 08 Jul 2022 06:07:49 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Subject: [PATCH v3 0/5] btrfs: qgroup: address the performance penalty for subvolume dropping Date: Fri, 8 Jul 2022 14:07:25 +0800 Message-Id: X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Changelog: v2: - Split /sys/fs/btrfs//qgroups/qgroup_flags into two entries - Update the cover letter to explain the drop_subtree_threshold better v3: - Rebased to latest misc-next Btrfs qgroup has a long history of bringing huge performance penalty, from subvolume dropping to balance. Although we solved the problem for balance, but the subvolume dropping problem is still unresolved, as we really need to do all the costly backref for all the involved subtrees, or qgroup numbers will be inconsistent. But the performance penalty is sometimes too big, so big that it's better just to disable qgroup, do the drop, then do the rescan. This patchset will address the problem by introducing a user configurable sysfs interface, to allow certain high subtree dropping to mark qgroup inconsistent, and skip the whole accounting. The following things are needed for this objective: - New qgroups attributes Instead of plain qgroup kobjects, we need extra attributes like drop_subtree_threshold. This patchset will introduce two new attributes to the existing qgroups kobject: * qgroups_flags To indicate the qgroup status flags like ON, RESCAN, INCONSISTENT. * drop_subtree_threshold To show the subtree dropping level threshold. The default value is BTRFS_MAX_LEVEL (8), which means all subtree dropping will go through the qgroup accounting, while costly it will try to keep qgroup numbers as consistent as possible. Users can specify values like 3, meaning any subtree which is at level 3 or higher will mark qgroup inconsistent and skip all the costly accounting. NOTE: if a snapshot is create with tree root level 3, dropping the snapshot with drop_subtree_threshold 3 will not mark the qgroup inconsistent. Since the level threshold is for shared subtree node, not the snapshot root node. In the case of newly created snapshot, only its (root level - 1) tree blocks are shared subtrees. This only affects subvolume dropping. - Skip qgroup accounting when the numbers are already inconsistent But still keeps the qgroup relationship correct, thus users can keep its qgroup organization while do the rescan later. This sysfs interface needs user space tools to monitor and set the values for each btrfs. And it's also user space daemon's responsibility to save the drop_subtree_threshold values. As introducing a new on-disk format just for qgroup is a little overkilled to an optional feature to me. Currently the target user space tool is snapper, which by default utilizes qgroups for its space-aware snapshots reclaim mechanism. Qu Wenruo (5): btrfs: sysfs: introduce qgroup global attribute groups btrfs: introduce BTRFS_QGROUP_STATUS_FLAGS_MASK for later expansion btrfs: introduce BTRFS_QGROUP_RUNTIME_FLAG_CANCEL_RESCAN btrfs: introduce BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING to skip qgroup accounting btrfs: skip subtree scan if it's too high to avoid low stall in btrfs_commit_transaction() fs/btrfs/ctree.h | 1 + fs/btrfs/disk-io.c | 1 + fs/btrfs/qgroup.c | 84 ++++++++++++++++++------ fs/btrfs/qgroup.h | 3 + fs/btrfs/sysfs.c | 112 ++++++++++++++++++++++++++++++-- include/uapi/linux/btrfs_tree.h | 4 ++ 6 files changed, 180 insertions(+), 25 deletions(-) -- 2.36.1