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 6FE02C433F5 for ; Tue, 18 Jan 2022 07:19:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244571AbiARHTY (ORCPT ); Tue, 18 Jan 2022 02:19:24 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:51020 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229661AbiARHTY (ORCPT ); Tue, 18 Jan 2022 02:19:24 -0500 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-out1.suse.de (Postfix) with ESMTPS id 94B30212C3; Tue, 18 Jan 2022 07:19:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1642490362; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=mwrMm9p0XKm29fkZlYtvb/i6y3gRyXzoJRGx3A3cGZo=; b=fIzWN9k1lgiNdVnTrAir1QaSO4VQyM4CrKcZm9O9Adgdm9ShVNL1G7XqNXWfu4jlIe/cqY fim0Pgo6tWN+s4P4gaQmsF4qoeVeXwg42hNpjXeye0RkNw1aqnARt0nn+RDJGGL0N/QkfX Q2mJCGyLGEjzcRz+pQ/A2agYbgpTSpY= 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 B87B51332F; Tue, 18 Jan 2022 07:19:21 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id KS9hIflp5mF5RQAAMHmgww (envelope-from ); Tue, 18 Jan 2022 07:19:21 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Anthony Ruhier Subject: [PATCH v2] btrfs: defrag: fix the wrong number of defragged sectors Date: Tue, 18 Jan 2022 15:19:04 +0800 Message-Id: <20220118071904.29991-1-wqu@suse.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org [BUG] There are users using autodefrag mount option reporting obvious increase in IO: > If I compare the write average (in total, I don't have it per process) > when taking idle periods on the same machine: > Linux 5.16: > without autodefrag: ~ 10KiB/s > with autodefrag: between 1 and 2MiB/s. > > Linux 5.15: > with autodefrag:~ 10KiB/s (around the same as without > autodefrag on 5.16) [CAUSE] When autodefrag mount option is enabled, btrfs_defrag_file() will be called with @max_sectors = BTRFS_DEFRAG_BATCH (1024) to limit how many sectors we can defrag in one try. And then use the number of sectors defragged to determine if we need to re-defrag. But commit b18c3ab2343d ("btrfs: defrag: introduce helper to defrag one cluster") uses wrong unit to increase @sectors_defragged, which should be in unit of sector, not byte. This means, if we have defragged any sector, then @sectors_defragged will be >= sectorsize (normally 4096), which is larger than BTRFS_DEFRAG_BATCH. This makes the @max_sectors check in defrag_one_cluster() to underflow, rendering the whole @max_sectors check useless. Thus causing way more IO for autodefrag mount options, as now there is no limit on how many sectors can really be defragged. [FIX] Fix the problems by: - Use sector as unit when increaseing @sectors_defragged - Include @sectors_defragged > @max_sectors case to break the loop - Add extra comment on the return value of btrfs_defrag_file() Reported-by: Anthony Ruhier Fixes: b18c3ab2343d ("btrfs: defrag: introduce helper to defrag one cluster") Signed-off-by: Qu Wenruo --- Changelog: v2: - Update the commit message to include the root cause of extra IO - Keep @sectors_defragged update where it is Since the over-reported @sectors_defragged is not the real reason, keep the patch smaller. --- fs/btrfs/ioctl.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 6ad2bc2e5af3..2a77273d91fe 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1442,8 +1442,8 @@ static int defrag_one_cluster(struct btrfs_inode *inode, list_for_each_entry(entry, &target_list, list) { u32 range_len = entry->len; - /* Reached the limit */ - if (max_sectors && max_sectors == *sectors_defragged) + /* Reached or beyond the limit */ + if (max_sectors && *sectors_defragged >= max_sectors) break; if (max_sectors) @@ -1465,7 +1465,8 @@ static int defrag_one_cluster(struct btrfs_inode *inode, extent_thresh, newer_than, do_compress); if (ret < 0) break; - *sectors_defragged += range_len; + *sectors_defragged += range_len >> + inode->root->fs_info->sectorsize_bits; } out: list_for_each_entry_safe(entry, tmp, &target_list, list) { @@ -1484,6 +1485,9 @@ static int defrag_one_cluster(struct btrfs_inode *inode, * @newer_than: minimum transid to defrag * @max_to_defrag: max number of sectors to be defragged, if 0, the whole inode * will be defragged. + * + * Return <0 for error. + * Return >=0 for the number of sectors defragged. */ int btrfs_defrag_file(struct inode *inode, struct file_ra_state *ra, struct btrfs_ioctl_defrag_range_args *range, -- 2.34.1