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 1D08EC4167B for ; Tue, 12 Apr 2022 08:57:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1386408AbiDLI5z (ORCPT ); Tue, 12 Apr 2022 04:57:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1359386AbiDLHm7 (ORCPT ); Tue, 12 Apr 2022 03:42:59 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B44EB2CC92; Tue, 12 Apr 2022 00:22:01 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5BF19B81B60; Tue, 12 Apr 2022 07:22:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA537C385A1; Tue, 12 Apr 2022 07:21:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649748119; bh=oVLVH4dSiXl6ZrohuS/jFnrjBXXcyG7ewltwzTF8/vg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=B4xkqMnbkuJZNxSwkicNWWjdhRWBPJseJrp3DOrT26MpLBDWM2y9Ax5BT2Tckphp6 +K3vOnkScPRtLz4A8Nkyfhe0SFVBo0VuNblf1WAKXRGACZ63o+THWAsDaiJHK52VVT ZFu3c2yGmj53OSf9YnC3ai4HQmM3k7dYyPn6+RL4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Filipe Manana , Qu Wenruo , David Sterba Subject: [PATCH 5.17 286/343] btrfs: avoid defragging extents whose next extents are not targets Date: Tue, 12 Apr 2022 08:31:44 +0200 Message-Id: <20220412062959.581114826@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412062951.095765152@linuxfoundation.org> References: <20220412062951.095765152@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Qu Wenruo commit 75a36a7d3ea904cef2e5b56af0c58cc60dcf947a upstream. [BUG] There is a report that autodefrag is defragging single sector, which is completely waste of IO, and no help for defragging: btrfs-cleaner-808 defrag_one_locked_range: root=256 ino=651122 start=0 len=4096 [CAUSE] In defrag_collect_targets(), we check if the current range (A) can be merged with next one (B). If mergeable, we will add range A into target for defrag. However there is a catch for autodefrag, when checking mergeability against range B, we intentionally pass 0 as @newer_than, hoping to get a higher chance to merge with the next extent. But in the next iteration, range B will looked up by defrag_lookup_extent(), with non-zero @newer_than. And if range B is not really newer, it will rejected directly, causing only range A being defragged, while we expect to defrag both range A and B. [FIX] Since the root cause is the difference in check condition of defrag_check_next_extent() and defrag_collect_targets(), we fix it by: 1. Pass @newer_than to defrag_check_next_extent() 2. Pass @extent_thresh to defrag_check_next_extent() This makes the check between defrag_collect_targets() and defrag_check_next_extent() more consistent. While there is still some minor difference, the remaining checks are focus on runtime flags like writeback/delalloc, which are mostly transient and safe to be checked only in defrag_collect_targets(). Link: https://github.com/btrfs/linux/issues/423#issuecomment-1066981856 CC: stable@vger.kernel.org # 5.16+ Reviewed-by: Filipe Manana Signed-off-by: Qu Wenruo Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/ioctl.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1215,7 +1215,7 @@ static u32 get_extent_max_capacity(const } static bool defrag_check_next_extent(struct inode *inode, struct extent_map *em, - bool locked) + u32 extent_thresh, u64 newer_than, bool locked) { struct extent_map *next; bool ret = false; @@ -1225,11 +1225,12 @@ static bool defrag_check_next_extent(str return false; /* - * We want to check if the next extent can be merged with the current - * one, which can be an extent created in a past generation, so we pass - * a minimum generation of 0 to defrag_lookup_extent(). + * Here we need to pass @newer_then when checking the next extent, or + * we will hit a case we mark current extent for defrag, but the next + * one will not be a target. + * This will just cause extra IO without really reducing the fragments. */ - next = defrag_lookup_extent(inode, em->start + em->len, 0, locked); + next = defrag_lookup_extent(inode, em->start + em->len, newer_than, locked); /* No more em or hole */ if (!next || next->block_start >= EXTENT_MAP_LAST_BYTE) goto out; @@ -1241,6 +1242,13 @@ static bool defrag_check_next_extent(str */ if (next->len >= get_extent_max_capacity(em)) goto out; + /* Skip older extent */ + if (next->generation < newer_than) + goto out; + /* Also check extent size */ + if (next->len >= extent_thresh) + goto out; + ret = true; out: free_extent_map(next); @@ -1446,7 +1454,7 @@ static int defrag_collect_targets(struct goto next; next_mergeable = defrag_check_next_extent(&inode->vfs_inode, em, - locked); + extent_thresh, newer_than, locked); if (!next_mergeable) { struct defrag_target_range *last;