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 B6F84EB64DA for ; Mon, 26 Jun 2023 12:20:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230471AbjFZMTy (ORCPT ); Mon, 26 Jun 2023 08:19:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53596 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229698AbjFZMT3 (ORCPT ); Mon, 26 Jun 2023 08:19:29 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAA3E10DE for ; Mon, 26 Jun 2023 05:19:07 -0700 (PDT) Received: from dggpemm500011.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QqRdx6QH2zlVwY; Mon, 26 Jun 2023 20:16:21 +0800 (CST) Received: from [10.174.179.155] (10.174.179.155) by dggpemm500011.china.huawei.com (7.185.36.110) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Mon, 26 Jun 2023 20:19:03 +0800 Message-ID: Date: Mon, 26 Jun 2023 20:19:03 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:104.0) Gecko/20100101 Thunderbird/104.0 To: , , , , Joe Thornber CC: , Hou Tao , "zhangyi (F)" , "yukuai (C)" , yangerkun From: Li Lingfeng Subject: [Question] Can DATA_DEV_BLOCK_SIZE_MIN_SECTORS be set to a smaller value Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.155] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500011.china.huawei.com (7.185.36.110) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello: Recently, I found that the used space of the thin-pool will keep rising if I use dm-thin as follow: // create dm-thin dmsetup create linear_1 --table "0 2097152 linear /dev/sdc 0" dmsetup create linear_2 --table "0 16777216  linear /dev/sdc 2097153" dd if=/dev/zero of=/dev/mapper/linear_1 bs=4096 count=1 dmsetup create pool --table "0 16777216 thin-pool /dev/mapper/linear_1 /dev/mapper/linear_2 128 0 1 skip_block_zeroing" dmsetup message /dev/mapper/pool 0 "create_thin 0" dmsetup create thin --table "0 14680064 thin /dev/mapper/pool 0" // mkfs and mount with discard mkfs.ext4 /dev/mapper/thin mount /dev/mapper/thin /mnt/test -o discard cd /mnt/test // create a file(17KB) dd if=/dev/random of=testfile bs=1k count=17 oflag=direct sync // truncate the file and write it for many times dd if=/dev/random of=testfile bs=1k count=17 oflag=direct sync ... Ext4 will issue discard IO to dm-thin when truncating file. However, DATA_DEV_BLOCK_SIZE_MIN_SECTORS is set as 64KB which means the discard covers less than a block when I truncating a 17KB file. As the result of it, discard bio will end in process_discard_bio(), and more and more blocks will leak. I'm curious about the reason behind setting DATA_DEV_BLOCK_SIZE_MIN_SECTORS to 64KB. Is there any specific consideration for this? Would it be possible to set this minimum limit to a smaller value, such as 4KB?