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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 3DAD0C5ACAE for ; Thu, 12 Sep 2019 10:02:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 084AE206A5 for ; Thu, 12 Sep 2019 10:02:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="heWEJ4AW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730805AbfILKCc (ORCPT ); Thu, 12 Sep 2019 06:02:32 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:60772 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730450AbfILKCb (ORCPT ); Thu, 12 Sep 2019 06:02:31 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x8C9x2lo149465; Thu, 12 Sep 2019 10:02:28 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=content-type : mime-version : subject : from : in-reply-to : date : cc : content-transfer-encoding : message-id : references : to; s=corp-2019-08-05; bh=gOS/JzpofuPWWnz1j6wS+PSjm6MNZh5a4XhX3Ypy+ZY=; b=heWEJ4AWfHiC7ERcqVPusKcviC/iKyCxAdXvHoe9DL3ZCzZIcrBFddnweqhbZRxskK4V 3wZUHvWyihY2zIwyiiIstxhEO4kGOIHPWC0w7nv5m3Mq5/YK6YFdVj7rj2MSQNL8h+fp gMwnoB5n30WssnmcwKYQkdpTF/02cjU9A+nlbFTycDRmei2nrebA3lItqUr8I1gGJawJ y4Cz6q7yh4c3UyGj3j/cixW5U4fYmp+eiCOAWKr+/NxpL0WnVupvw5s+2DSfZkrOFJdd IczNcVeY5UO9eROm0Vy2cGgZxx1wEp+0Z6LuX24Y1by79UQ8iv7QVp5xLf55Xg1RLQn2 oQ== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2120.oracle.com with ESMTP id 2uw1jkqd7a-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 12 Sep 2019 10:02:28 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x8C9x4uT105042; Thu, 12 Sep 2019 10:00:28 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userp3020.oracle.com with ESMTP id 2uy33c1nhy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 12 Sep 2019 10:00:27 +0000 Received: from abhmp0001.oracle.com (abhmp0001.oracle.com [141.146.116.7]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x8CA0QdN021870; Thu, 12 Sep 2019 10:00:26 GMT Received: from [10.190.130.61] (/192.188.170.109) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 12 Sep 2019 03:00:26 -0700 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\)) Subject: Re: [PATCH RFC v2 0/2] readmirror feature From: Anand Jain In-Reply-To: <20190912095021.htmpvvowdprc2jhv@MacBook-Pro-91.local> Date: Thu, 12 Sep 2019 18:00:21 +0800 Cc: Anand Jain , Eli V , linux-btrfs Content-Transfer-Encoding: quoted-printable Message-Id: References: <20190826090438.7044-1-anand.jain@oracle.com> <20190911184229.gl7tu3igtuuepcvm@macbook-pro-91.dhcp.thefacebook.com> <20190911191656.mrmfyhvy3latjwid@macbook-pro-91.dhcp.thefacebook.com> <2f10bebf-bc63-fe9e-d7d3-06b3113bc95c@oracle.com> <20190912095021.htmpvvowdprc2jhv@MacBook-Pro-91.local> To: Josef Bacik X-Mailer: Apple Mail (2.3445.104.11) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9377 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909120105 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9377 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909120105 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org > On 12 Sep 2019, at 5:50 PM, Josef Bacik wrote: >=20 > On Thu, Sep 12, 2019 at 03:41:42PM +0800, Anand Jain wrote: >>=20 >>=20 >> Thanks for the comments. More below. >>=20 >> On 12/9/19 3:16 AM, Josef Bacik wrote: >>> On Wed, Sep 11, 2019 at 03:13:21PM -0400, Eli V wrote: >>>> On Wed, Sep 11, 2019 at 2:46 PM Josef Bacik = wrote: >>>>>=20 >>>>> On Mon, Aug 26, 2019 at 05:04:36PM +0800, Anand Jain wrote: >>>>>> Function call chain __btrfs_map_block()->find_live_mirror() uses >>>>>> thread pid to determine the %mirror_num when the mirror_num=3D0. >>>>>>=20 >>>>>> This patch introduces a framework so that we can add policies to = determine >>>>>> the %mirror_num. And also adds the devid as the readmirror = policy. >>>>>>=20 >>>>>> The new property is stored as an item in the device tree as show = below. >>>>>> (BTRFS_READMIRROR_OBJECTID, BTRFS_PERSISTENT_ITEM_KEY, devid) >>>>>>=20 >>>>>> To be able to set and get this new property also introduces new = ioctls >>>>>> BTRFS_IOC_GET_READMIRROR and BTRFS_IOC_SET_READMIRROR. The ioctl = argument >>>>>> is defined as >>>>>> struct btrfs_ioctl_readmirror_args { >>>>>> __u64 type; /* RW */ >>>>>> __u64 device_bitmap; /* RW */ >>>>>> } >>>>>>=20 >>>>>> An usage example as follows: >>>>>> btrfs property set /btrfs readmirror devid:1,3 >>>>>> btrfs property get /btrfs readmirror >>>>>> readmirror devid:1 3 >>>>>> btrfs property set /btrfs readmirror "" >>>>>> btrfs property get /btrfs readmirror >>>>>> readmirror default >>>>>>=20 >>>>>> This patchset has been tested completely, however marked as RFC = for the >>>>>> following reasons and comments on them (or any other) are = appreciated as >>>>>> usual. >>>>>> . The new objectid is defined as >>>>>> #define BTRFS_READMIRROR_OBJECTID -1ULL >>>>>> Need consent we are fine to use this value, and with this = value it >>>>>> shall be placed just before the DEV_STATS_OBJECTID item which = is more >>>>>> frequently used only during the device errors. >>>>>>=20 >>>>>> . I am using a u64 bitmap to represent the devices id, so the = max device >>>>>> id that we could represent is 63, its a kind of limitation = which should >>>>>> be addressed before integration, I wonder if there is any = suggestion? >>>>>> Kindly note that, multiple ioctls with each time representing = a set of >>>>>> device(s) is not a choice because we need to make sure the = readmirror >>>>>> changes happens in a commit transaction. >>>>>>=20 >>>>>> v1->RFC v2: >>>>>> . Property is stored as a dev-tree item instead of root inode = extended >>>>>> attribute. >>>>>> . Rename BTRFS_DEV_STATE_READ_OPRIMIZED to = BTRFS_DEV_STATE_READ_PREFERRED. >>>>>> . Changed format specifier from devid1,2,3.. to devid:1,2,3.. >>>>>>=20 >>>>>> RFC->v1: >>>>>> Drops pid as one of the readmirror policy choices and as usual = remains >>>>>> as default. And when the devid is reset the readmirror policy = falls back >>>>>> to pid. >>>>>> Drops the mount -o readmirror idea, it can be added at a later = point of >>>>>> time. >>>>>> Property now accepts more than 1 devid as readmirror device. As = shown >>>>>> in the example above. >>>>>>=20 >>>>>=20 >>>>> This is a lot of infrastructure >>=20 >> Ok. Any idea on a better implementation? >> How about extended attribute approach? v1 patches proposed >> it, but it abused the extended attribute as commented here [1] >> and v2 got changed to an item-key. >>=20 >> [1] >> = https://lore.kernel.org/linux-btrfs/be68e6ea-00bc-b750-25e1-9c584b99308f@g= mx.com/ >>=20 >=20 > That's a NAK on the prop interface. This is a fs wide policy, not a > directory/inode policy. >=20 >>=20 >>>>> to just change which mirror we read to based on >>>>> some arbitrary user policy. I assume this is to solve the case = where you have >>>>> slow and fast disks, so you can always read from the fast disk? = And then it's >>>>> only used in RAID1, so the very narrow usecase of having a RAID1 = setup with a >>>>> SSD and a normal disk? I'm not seeing a point to this much code = for one >>>>> particular obscure setup. Thanks, >>>>>=20 >>>>> Josef >>>>=20 >>>> Not commenting on the code itself, but as a user I see this SSD = RAID1 >>>> acceleration as a future much have feature. It's only obscure at = the >>>> moment because we don't have code to take advantage of it. But on >>>> large btrfs filesystems with hundreds of GB of metadata, like I = have >>>> for backups, the usability of the filesystem is dramatically = improved >>>> having the metadata on an SSD( though currently only half of the = time >>>> due to the even/odd pid distribution.) >>>=20 >>> But that's different from a mirror. 100% it would be nice to say = "put my >>> metadata on the ssd, data elsewhere". That's not what this patch is = about, this >>> patch is specifically about changing which drive we choose in a = mirrored setup, >>> which is super unlikely to mirror a SSD with a slow drive, cause = it's just going >>> to be slow no matter what. Sure we could make it so reads always go = to the SSD, >>> but we can accomplish that by just adding a check for nonrotational = in the code, >>> and then we don't have to encode all this nonsense in the file = system. Thanks, >>=20 >> I wrote about the readmirror policy framework here[2], >> I forgot to link it here, sorry about that, my mistake. >>=20 >> [2] >>=20 >> = https://lore.kernel.org/linux-btrfs/1552989624-29577-1-git-send-email-anan= d.jain@oracle.com/ >>=20 >> Readmirror policy is for raid1, raid10 and future N way mirror. >> Yes for now its only for raid1. >>=20 >> Here the idea is to create a framework so that readmirror policy >> can be configured as needed. And nonrotational can be one such = policy. >>=20 >> The example of hard-coded nonrotational policy does not work in case >> of ssd and a remote iscsi ssd, OR in case of local ssd and a NVME = block >> device, as all these are still nonrotational devices. So hard-coded >> policy is not a good idea. If we have to hardcode then there is = Q-depth >> based readmirror routing is better (patch in the ML), but that is >> not good enough, because some configs wants it based on the disk-LBA >> so that SAN storage target cache is balanced and not duplicated. >> So in short it must be a configurable policy. >>=20 >=20 > Again, if you are mixing disk types you likely always want = non-rotational, but > still mixing different speed devices in a mirror setup is just asking = for weird > latency problems. I don't think solving this use case is necessary. = If you mix > ssd + network device in a serious production setup then you probably = should be > fired cause you don't know what you are doing. Having the generic > "nonrotational gets priority" is going to cover 99% of the actual use = cases that > make sense. >=20 > The SAN usecase I can sort of see, but again I don't feel like it's a = problem we > need to solve with on-disk format. Add a priority to sysfs so you can = change it > with udev or something on the fly. Thanks, >=20 =20 Ok. Sysfs is fine however we need configuration to be persistent across = reboots. Any idea? Thanks, Anand > Josef