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 E2D37EB64DA for ; Mon, 26 Jun 2023 12:28:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230400AbjFZM22 (ORCPT ); Mon, 26 Jun 2023 08:28:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230112AbjFZM17 (ORCPT ); Mon, 26 Jun 2023 08:27:59 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F78530EC for ; Mon, 26 Jun 2023 05:25:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687782345; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kDHI+2QYFaocdNjg/agTcKpYLb3vBgPdGHQo8p/fVPI=; b=YeX0/mqN/Vdim4pahGW8pwa7zHG2qgLbVn4T5v18xwGC43XLRnhJH/nAEN8b9WrLAfNlhy 9M1xgCdv4OBbijkeS/kRxAZtcSqe5wjp//7ny6WIbEzWdgn39Ep3gwcm6E73Nn2lL7/ASi 7SFMUguFrLMOrgoCZmt2SAUuSex+P6w= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-64-IfVzUUmpPvScdOPPyHm_DQ-1; Mon, 26 Jun 2023 08:25:33 -0400 X-MC-Unique: IfVzUUmpPvScdOPPyHm_DQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E69078A7F72; Mon, 26 Jun 2023 12:25:29 +0000 (UTC) Received: from [10.45.226.134] (unknown [10.45.226.134]) by smtp.corp.redhat.com (Postfix) with ESMTP id 65629200C0F2; Mon, 26 Jun 2023 12:25:28 +0000 (UTC) Message-ID: <2096ab6c-7a14-85bb-22d6-3189507c4783@redhat.com> Date: Mon, 26 Jun 2023 14:25:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.12.0 Subject: Re: [dm-devel] [Question] Can DATA_DEV_BLOCK_SIZE_MIN_SECTORS be set to a smaller value To: Li Lingfeng , dm-devel@redhat.com Cc: linux-kernel@vger.kernel.org References: Content-Language: en-US From: Zdenek Kabelac In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dne 26. 06. 23 v 14:19 Li Lingfeng napsal(a): > 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? Hi The minimal chunksize for thin-pool was selected to  64K - smaller value would cause major expansion in the used 'metadata' size and further slowdown of metadata manipulation - so the 64K was set as minimal size. Regards Zdenek