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=-2.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 7E073C433DB for ; Sat, 23 Jan 2021 11:00:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B14423428 for ; Sat, 23 Jan 2021 11:00:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726609AbhAWLA3 (ORCPT ); Sat, 23 Jan 2021 06:00:29 -0500 Received: from mout.gmx.net ([212.227.15.15]:53325 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726379AbhAWLA2 (ORCPT ); Sat, 23 Jan 2021 06:00:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1611399534; bh=xkv99fZAucZ3tYsKqUqWWbET7N3pjUFCWDxs9SX7Z6c=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=PNLvoJhw+iY85QUDpQ0RtpZXKVzIcfFpHzITJsi49xCVoG+w9hVNv0G2avgnAceWb EOiwKeWk7DTNXuDbBgvtbRqMIGQYN03lBoe2QSRjl7emVqEosDeGoCnr6VpR/z5b1L SAOFuGfTJ4YfQqAU6ggwwx+FFlTjMnqWIjgMKtvA= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([149.28.201.231]) by mail.gmx.net (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1MWASe-1lWXup0czS-00Xa9N; Sat, 23 Jan 2021 11:58:53 +0100 Subject: Re: Unexpected reflink/subvol snapshot behaviour To: Roman Mamedov Cc: Dave Chinner , linux-btrfs@vger.kernel.org References: <20210121222051.GB4626@dread.disaster.area> <58c9d792-5af4-7b54-2072-77230658e677@gmx.com> <20210123153933.534a43ea@natsu> From: Qu Wenruo Message-ID: Date: Sat, 23 Jan 2021 18:58:49 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210123153933.534a43ea@natsu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:YJCgSHnBCbjU+efMxJomsvuF2BjFDJkRu/9d2gHlA1eXE55xy2c 1bWU4LG7e/yxMybZ2iZbpjGHrVKEgJ14VVaq4qD8FsueRB3/PSC0E0/9yS/JiCiuKQLLcGW cyC1FuPg92Nn1Hmx313AWTtfv+Jj5Lg4P4UF5qTeVgkKqGNzrfQykPtNYIXCPX56g6jGhG3 XS22fUhVeSUTj+sybn5Rg== X-UI-Out-Filterresults: notjunk:1;V03:K0:3gmwWl2lMZM=:ZBnDqQqmQcENmLciHNRUcr QwcDGAsKDj7aiFDSsoSCSqq5MxRb5/8Z+kRhD8jMN+YKyQoF9QNU7IAuLhUIO4UmVL75LzWpZ lyuQaLc+DpMrwInyOXHiK4BAiilU8xyM6T4NoV4+PyHraI6QPeicRDfPHpJOkokHY1lfOf7lF NENqHRuwxmblOiUVo72nfY2W1NF7FoW9T5MiraZq0whb79pS3MuRAYOnlL5BGoUfnU3l9RTTJ yS2lrova46qYxdKepiWC8LL8zjzTF6dZYYulRqFOi70mT48fYPfoTyI7SkGLyQsMGmbD8AYJ1 njWX7nuYrZNuFzZ7OCG+Qct1x3COl08DBALh/fNHnRndRiOIUD09IJ6It+JWfBTNjwan6wuyZ 6SB/96o5oD9Ig0+Q7hjH+SE5yfvtF+C4NJycjD8yn7VdKEHa6btbNB6AWmruUhZ5c6xa55rY5 /bhBJxO5TryYFHQxfwERw3Ob2lV3KybTgyzexjskhau+4PNqw94ZiEsJcIzreLDcBnd1z0baK imzk9kM2R8OuULeAT+co0Zqjhasbm1QijOprUfcScBL9VorF7xnTriLpPfhZO6j0AyTEZKN90 PA4lFUUu1v18VKpiOecXBiCXBvOGo5/3LJOeakjHuQ3/ok4BP5E8eMwMSiAtZYexQ2+9BZNmD /QdPFrACRYgMa3GWbn/bKGVzllg+6coiXtzctAeh3gD1enELIclvATWF5h1lVlQKnaGPon9YW a5BlusV/QjtJGOTnFTXNIGi+jTCy9LesiQ5+N76zZxkhYV/MQ18y7/v/fUr81/D3+brB8K7CE KTBX3lRwxGBflqSxBkoqhbGLuwKipYMHMJ+LxXPNCm4HDYLbxuG5e6GlyWcpBSxoqXY/OYTSZ IF0AtkQ3vg/L6OCK6LvA== Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2021/1/23 =E4=B8=8B=E5=8D=886:39, Roman Mamedov wrote: > On Sat, 23 Jan 2021 16:42:33 +0800 > Qu Wenruo wrote: > >> For the worst case, btrfs can allocate a 128 MiB file extent, and have >> good luck to write 127MiB into the extent. It will take 127MiB + 128MiB >> space, until the last 1MiB of the original extent get freed, the full >> 128MiB can be freed. > > Does it mean enabling compression actually mitigates this issue as a > side-effect? Since each extent will be limited to only 128K. Yes! Compression brings the side effect of reducing the maximum data extent size, thus mitigates the problem by 1024. But the problem is still there. Thanks, Qu > > What are the typical extent sizes without compression? >