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 X-Spam-Level: X-Spam-Status: No, score=-12.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9CFE5C4361B for ; Thu, 17 Dec 2020 12:55:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5D92423884 for ; Thu, 17 Dec 2020 12:55:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726291AbgLQMzC (ORCPT ); Thu, 17 Dec 2020 07:55:02 -0500 Received: from mx2.suse.de ([195.135.220.15]:36834 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725871AbgLQMzB (ORCPT ); Thu, 17 Dec 2020 07:55:01 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1608209654; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=32ruNfwarHqR3vsd4V6oonkaQd9dnv5u3/MqUm6mZas=; b=hOzOohEA9CXTs997qVNRbgBt/1yCZKTaI0cYa6sKWnzGsbXUOwA/Vr3roFOSp3NbQM6PWa 4CpucZ8mMyrLtzwsAlbXf2EnIjuAIxE53rqYo4Extd6ycfE8IIJ8km53COW6zzIOIu1yR0 0b2QUtlG/2Tq3NIxjuamaOJvXiTSUZs= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9381EAC7F; Thu, 17 Dec 2020 12:54:14 +0000 (UTC) Subject: Re: [PATCH v2 2/2] btrfs: account for new extents being deleted in total_bytes_pinned To: Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: <0826b647d5dd12f8134614e05519156d9351f2c1.1608137123.git.josef@toxicpanda.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <0826b647d5dd12f8134614e05519156d9351f2c1.1608137123.git.josef@toxicpanda.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 16.12.20 г. 18:46 ч., Josef Bacik wrote: > My recent set of patches to reduce lock contention on the extent root by > running delayed refs resulted in a regression in generic/371. This test > fallocate()'s the fs until it's full, deletes all the files, and then > tries to fallocate() until full again. > > Before my delayed refs patches we would run all of the delayed refs > during flushing, and then would commit the transaction because we had > plenty of pinned space to recover in order to allocate. However my > patches made it so we weren't running the delayed refs as aggressively, > which meant that we appeared to have less pinned space when we were > deciding to commit the transaction. > > We use the space_info->total_bytes_pinned to approximate how much space > we have pinned. It's approximate because if we remove a reference to an > extent we may free it, but there may be more references to it than we > know of at that point, but we account it as pinned at the creation time, > and then it's properly accounted when the delayed ref runs. > > The way we account for pinned space is if the > delayed_ref_head->total_ref_mod is < 0, because that is clearly a > free'ing option. However there is another case, and that is where > ->total_ref_mod == 0 && ->must_insert_reserved == 1. > > When we allocate a new extent, we have ->total_ref_mod == 1 and we have > ->must_insert_reserved == 1. This is used to indicate that it is a > brand new extent and will need to have its extent entry added before we > modify any references on the delayed ref head. But if we subsequently > remove that extent reference, our ->total_ref_mod will be 0, and that > space will be pinned and freed. Accounting for this case properly > allows for generic/371 to pass with my delayed refs patches applied. > > It's important to note that this problem exists without my delayed refs > patches, it just was uncovered by them. > > Signed-off-by: Josef Bacik Reviewed-by: Nikolay Borisov