From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752794AbcIBNgF (ORCPT ); Fri, 2 Sep 2016 09:36:05 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:55327 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750969AbcIBNgB (ORCPT ); Fri, 2 Sep 2016 09:36:01 -0400 Subject: Re: [PATCH] btrfs: let btrfs_delete_unused_bgs() to clean relocated bgs To: Naohiro Aota , References: <1472802392-10851-1-git-send-email-naohiro.aota@hgst.com> CC: Chris Mason , David Sterba , From: Josef Bacik Message-ID: Date: Fri, 2 Sep 2016 09:35:31 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <1472802392-10851-1-git-send-email-naohiro.aota@hgst.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [107.15.72.49] X-ClientProxiedBy: BN6PR12CA0010.namprd12.prod.outlook.com (10.168.222.20) To MWHPR15MB1325.namprd15.prod.outlook.com (10.175.3.139) X-MS-Office365-Filtering-Correlation-Id: 2e3fb524-9620-4a8b-9e86-08d3d33610f7 X-Microsoft-Exchange-Diagnostics: 1;MWHPR15MB1325;2:KLZVFu1y9qcSe+7tmFkovJXy1FDRekSNDArlGa4W55xid+r3azeKq57xmR3D37FT2I3SzkUWYFEXPsL0NjS/7EJJk3YAYOBRDU3OtQDS+UKLXwgFofJivLIsRqs3TxQc1WOQZuziyxvt8syA6Qh5C9iPIgRSmPUvQO84k9TuMaxMg02FZSGYSaiY/1PMX9tX;3:v/1Dw5JrgFn9pfJRIDmhuXOoP4vhNpq+I450+VyXG/crYVid/kqI1APAla6pCfn0gBW8UrbQ6iNCs0fKqaVB6xBDwlNxaX/TZ54fnNY59nSlAgF+2D/cv6aGGmsk3irO;25:eSkHiWU79+ulCMESDb2WpAdJqJEljtAQKiyEXrTlCBBqxEy743MnNx+Ekjlbc8d2qONWhQDo/OkfTSuAQ3nKPiqI2oulLqJa2pwjUf5ok8nXr2OHqGFI5xM1UpJRRIb0rXTZl3Dup2+k97zo6c3Bv+Y1SnFZnnBckZEnXMfhtTOQWDyqF8MCAtcaEyPHZ7bpc5icia7SZ/vRe1HLuD3XGbZ09kuH742Kca3iGOY8H3CD6/e29RTk0LDuZ3r2hfQFEmnFgbfBKsSWIbzEZ/WvHLbJOLtBMXr/qGHr4BttBvpDEVzhK+DDzTiRtl1JypWpg9G2tvntB14grliGmFrWx/3/DrsB2HKGz3KT982FeVQsGFcwjk1OgmoyDVhoU5MVlceMxQd79+lCSe1XGY/TTNi0vKYow0PjdLIqOI0BGm0= X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:MWHPR15MB1325; X-Microsoft-Exchange-Diagnostics: 1;MWHPR15MB1325;31:advzCj5mozpyFsWpXI/SCpZvSG+MrUeqtiGXqhWjDRLjeXR3xSqAIyAaTRU2GIX/e5H57PJNhdgdKtG5iy5PLPZ/jduOsAAJD3dxsnQpyFM99i8cw27+CaOdFdXtWSQuaJJTfjWVOVUM9vDskxa2NQ8CIY4ZguWlnMtEZzoKJU7gpZ9lA95u/hwvByh5KhmFcJlFtxqDm+8ZKOPtPo5q0zfTibr79syihDxXt8Yv4Rw=;20:1dvcnRFYCDeRV++RklQms/BLujpSS/opy0x/wDZEDIWZoFLgiT9Ci3vMAwoFRjkSJHgfb/NNddLfTFyv2rDohhy7iiJJK29lR54ISnHcnsfQAfHGhnqV6BxKrSik3rd4T7+657zkj2eesr2WaOXWwE0ZtseQyR8lBRSF6nZ0k60=;4:rzRZUP3aTyw4++4vfUFQ+pb+sT+bbcnCsL4bkUbNVtRAYoPznOHzPNaXImuefcSHJDhBJ8Xjo3Xk615tPPHOmz2ntnBO7swDCRba8tnVl0/dyVn42mGrdptfk8V7DGAYFk1J0SSF4H+dlc/cjs8+wAyl4J1aalxaBDdwBr5dZi1ICBaBCFRGWW+ZmgsS7UpcZ/J9uDSXgjv4D8aT8SgqffdUEIms981UBL3rFP4sxsJukO4k5LkuqI5CpdGMCo6xeocNRj/hKYSOiVISBgVrINS7DXzsFt9y4A+0iTUn3UwRSc2SXdVijD1DRa8BYsLCoAJICwyB1qPYfe/t7PtW9bQwHs7D8JzYlBPQeOTOEElRqqRF2LOl5seKXW3gCZS4D56TKHYvLKCmyyFJLxzMRg== X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:; X-Exchange-Antispam-Report-CFA-Test: BCL:0;PCL:0;RULEID:(6040176)(601004)(2401047)(8121501046)(5005006)(10201501046)(3002001);SRVR:MWHPR15MB1325;BCL:0;PCL:0;RULEID:;SRVR:MWHPR15MB1325; X-Forefront-PRVS: 00531FAC2C X-Forefront-Antispam-Report: SFV:NSPM;SFS:(10019020)(4630300001)(979002)(6009001)(6069001)(7916002)(24454002)(189002)(199003)(377454003)(31686004)(42186005)(586003)(3846002)(6116002)(101416001)(4001350100001)(8676002)(551934003)(5001770100001)(92566002)(81166006)(230700001)(81156014)(65806001)(47776003)(66066001)(97736004)(65956001)(23746002)(5660300001)(65826007)(2950100001)(77096005)(305945005)(7846002)(7736002)(83506001)(76176999)(68736007)(54356999)(4326007)(50986999)(31696002)(189998001)(2906002)(86362001)(36756003)(50466002)(64126003)(105586002)(106356001)(33646002)(969003)(989001)(999001)(1009001)(1019001);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1325;H:localhost.localdomain;FPR:;SPF:None;PTR:InfoNoRecords;MX:1;A:1;LANG:en; X-Microsoft-Exchange-Diagnostics: =?Windows-1252?Q?1;MWHPR15MB1325;23:D3eefHaT+MlyvtZopAQ0PwZx4eiCJlnl9eopc?= =?Windows-1252?Q?8x+SGAuueB6GImeYDepJ5MlwT68gLnE5KihyqX8pwQwn1jsMOrb3FmN2?= =?Windows-1252?Q?89NJ4Hv3jk36sJAVy/D8ULU+A7skACJQH5tfhOjpUUTTF3ZXKttWgnWg?= =?Windows-1252?Q?HwG1kYJzlqk9/3GhxkgY8zeJgStlgZW6ordkvn6DfxYk9GqSakt2zLOV?= =?Windows-1252?Q?y2p7T4E12rX0ewl3aqOMZgUd7gtkuIPaiQssLq2OX1YnUFS37fkuMV7x?= =?Windows-1252?Q?kGaOHTTCBs3YyKcktYO6GbOdPvfIWbCNofECzqz9XQ5LExBqjArinB4d?= =?Windows-1252?Q?hacMUSYxpdTmrM0zw47qoibv6TezABpbx5uZmM1mkbll/OWRIAfUB16K?= =?Windows-1252?Q?oYJNnC/nLgslSAmz14FIBqPwY1TH6pRKcJ+SnQZ24+NudsKV/CEWBjL+?= =?Windows-1252?Q?GpLIw+mQZ986bUPd967HgOwxlZrCymQMAtgWkQD8pNFzTZqEXo6li3f8?= =?Windows-1252?Q?vTsbLbnuZSuOQtsAFWdmS5/EPQfk7SgJVJ7P73Ep5801ogXyF78owmhW?= =?Windows-1252?Q?j/jbw8NdG5qGIsDLaD+Agwrdc61sfsaUxy9mdQKVMCASQ1E63+o8OHac?= =?Windows-1252?Q?rjA2u/6EOEETnqswmY21wrb8HOX+AWNVyHsiSvHVA+SpugDRD2bmyd43?= =?Windows-1252?Q?7SN7dkxY8eTW0lF7LahrAMwgQOFmAIoL5nafajn8LwxhkUEysM/Mboll?= =?Windows-1252?Q?ND21YiFp292THthG1IsQ5yhHQisOSmJIS7nxYluWDnunUEIFQNrbeRk/?= =?Windows-1252?Q?VzH7ItoKselCG8jbeRvkgPlsjsPMepoQEIbAqBs3RK6dC68IWkNUeecA?= =?Windows-1252?Q?bUXxQ0/iccC26bBBJqA6Z7v4Ao0GdHg7s6lhyewAsBULF8SIBGLfc+G2?= =?Windows-1252?Q?nYHkXJOkTUkY7AOZU9EJziaBzs+fmlrDDNjUtXK4ALq5EA1JayXbv/pv?= =?Windows-1252?Q?C4axb5AzLjUdGyQ9c+sTg7E85fLgVO6vsqjk3xSe4FiwcpAlz6PQ7sQX?= =?Windows-1252?Q?BlbzIL+aZ9OCTIKsJLj0nY6jrpKhbor9eHhzTnYRLt+KWaG3ZbS80u7G?= =?Windows-1252?Q?XpaPLQpUsioSFEJQs/Dyzv31CKqj/f1IIXrUy4LSS4oMjfc+vKeIdhGu?= =?Windows-1252?Q?m9LnjQcdsNlg3/7xjkI10JuVHxgPcUp+Nc9Lc2LyaPX29DFA5Erttmcu?= =?Windows-1252?Q?vD3b1e57T6hAXWjMoaexcj9kaMJD08vNit7aHmrGcAPrD4pYh/2CjzGT?= =?Windows-1252?Q?Bw1vlNA75pzXl7zQ0w1FprHxXiEc8rOFlBysmH/mcoZp3evjK8kIA3rd?= =?Windows-1252?Q?6am7EkW+WQoc2mPN8EU+pk6xdvyrC9laZ4g09fnJKjkYHVIOs7PhMCDG?= =?Windows-1252?Q?Q8HBBqoknCJMz8YMfvEuT/DqchSLNVwWjMCV2izW5F3RVc46bPI8oEG8?= =?Windows-1252?Q?l8tqlw=3D?= X-Microsoft-Exchange-Diagnostics: 1;MWHPR15MB1325;6:kvDryXyAPvwk34BHkEegnTPLpNAMzBUTcb19Wq8RMb3jORrp04CjdVW8CaPnM8zUIzqJLz5Yic7lhkQrQq/IxYPjF6tDZaUxQVsKOXAJhmSp0JFMT4e1LMkTJTY3ozi1AfffyrX6yX2rvmEsbrx8+hPJTKc1eudDKzk2Ukg9j7gE/HoaEVlJiOZpjI1dZgi2igz5R0bPno5KyJ5EXljD1evuSuSRQqKd75RmGDLeU8n2J1c8hK3uAGLFLWpDbnhlGtRqvzGgtJJgN3aP2neTQ+YvV1SuF+ZPPwuZgFiuCgQ=;5:dzLl6r3KbB2gMFMN6FJJNlpdMWB9dFAOjHaLQWZJHYojW+aQtWNp74Kv8IWVNNdbxvkvoycJBR+T/3FeldGexSZzNEJN4yIN+WWN65PkoByn2s1Wow4jLRXfCp+9NqNUCFMVZi3VrCWyiPYum41PKg==;24:5fAYM6MOjQGmlI17VFwWNrNGueA73H5vd7HEKQ1HiawnS7wfO+UUWN7vvChWGSt66LuWlraFvkb7kc8E3v62UCktTdsDVQCUraIKJ8rn4/Y=;7:Cc0pe4fjf0moYM9pAG9z8XXG0w17EQ+OU3Zy6VYg+tVGE513qtSBEwD9Q9gP80QDJZehvH3Wkn9KqxCyyzKfNiDjR6aYozeAvGW8GXfyyu7dNhvu7dLd4oqO59kcznnIY5DfM91VZWnmUBHM+KR7fJpYznA7EsWI4OVJomwlJyuDuvPRrhnYkC6PXzyrHWxUadsaALg58fxUG/rER4tvAj+Hlb/QGi0HL1tgrT4yD6DhPcSzZowLXwBtkGJoyDzq SpamDiagnosticOutput: 1:99 SpamDiagnosticMetadata: NSPM X-Microsoft-Exchange-Diagnostics: 1;MWHPR15MB1325;20:BUZKY1mWXD8fUPdpj+5XzWJDSkJg9a9nGElx3YYq9t4vk6rMI15lAiPo6/9qd4529NJacjPtwJT8COXpOVnP86vjHXuiIfriOrQEhSOtYaR6VMgL2F+l6DMkFPodX6XJrDiO3koTSLvuW2EvZaLUdloznlCyW3S8giBhu9i558E= X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Sep 2016 13:35:54.8844 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1325 X-OriginatorOrg: fb.com X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-09-02_04:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/02/2016 03:46 AM, Naohiro Aota wrote: > Currently, btrfs_relocate_chunk() is removing relocated BG by itself. But > the work can be done by btrfs_delete_unused_bgs() (and it's better since it > trim the BG). Let's dedupe the code. > > While btrfs_delete_unused_bgs() is already hitting the relocated BG, it > skip the BG since the BG has "ro" flag set (to keep balancing BG intact). > On the other hand, btrfs cannot drop "ro" flag here to prevent additional > writes. So this patch make use of "removed" flag. > btrfs_delete_unused_bgs() now detect the flag to distinguish whether a > read-only BG is relocating or not. > This seems racey to me. We remove the last part of the block group, it ends up on the unused_bgs_list, we process this list, see that removed isn't set and we skip it, then later we set removed, but it's too late. I think the right way is to actually do a transaction, set ->removed, manually add it to the unused_bgs_list if it's not already, then end the transaction. This way we are guaranteed to have the bg on the list when it is ready to be removed. This is my analysis after looking at it for 10 seconds after being awake for like 30 minutes so if I'm missing something let me know. Thanks, Josef