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=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 29820ECDE20 for ; Thu, 12 Sep 2019 10:03:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA0E421479 for ; Thu, 12 Sep 2019 10:03:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=toxicpanda-com.20150623.gappssmtp.com header.i=@toxicpanda-com.20150623.gappssmtp.com header.b="GoNG0dJk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730969AbfILKDU (ORCPT ); Thu, 12 Sep 2019 06:03:20 -0400 Received: from mail-yw1-f66.google.com ([209.85.161.66]:34963 "EHLO mail-yw1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730580AbfILKDT (ORCPT ); Thu, 12 Sep 2019 06:03:19 -0400 Received: by mail-yw1-f66.google.com with SMTP id r134so3267969ywg.2 for ; Thu, 12 Sep 2019 03:03:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=toxicpanda-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ko5hvJzlDCDVhFBHtXdayYnzFcaFnGE/f+CpVHugumQ=; b=GoNG0dJk//s4BmjzwmqBf8DYO3fqsd1nhEm566//yiUOevE8q3RsKD+XTzrOnfcbtp Xu6V0C2VvP/EpqVUHQc6wiVFY+BePA+qkqwklAEaoi4z/SAAjdnjzQfbs/wIWihH2itQ AfNWDxcguAZ/vyaeiKRA90l13diF3koDUQJsVtO7ImnOQvnYDWdRPJUWoJc5OMMQNKcW XkRdIlCdBdRridr8lDc3ZnFDve+NXmuHQ9/vVNA6OO20a9d3C/VtiRjzOCkRA9g3FarX WQ3A5O7S0wH+hPjqX3E2VJ9Jsbp63kIs39XWx1fYBHqNJLUkZvU+hK/6/bFGigqlikmm zNrg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ko5hvJzlDCDVhFBHtXdayYnzFcaFnGE/f+CpVHugumQ=; b=ozUKx3qsGycgcra2opR5rtTM0KoZt4llsn8NR1xqsKzwZ/AJK+Id68OxNE+o1aK6Hs o5AolnIsCybN/pt3+mLWS2vLcjPjWPJYFdhQUfcEK9gccBX5GrEtdowcIMCrYd9SYcNv fpyXDNt+6zluhOAR4n5/F1nqMR7MhUDzNrTb2nWDPMKSSrv5qULM0XHJi9fvaBWg1Otk 5gE6m+r70yyVuJ5N8YpZjXT4gUXb6S0etueWt3D2rW0FAAir3Ghd9VxwXHeZXohMdIQF WJ0jsbeTcRzLrKbZQQlgwxTSV9KxyakQDKUjoS7dlknxDV4m1xMrfo4Y7AmAmAhj/pJe q/pw== X-Gm-Message-State: APjAAAUiv703CskGNFdtT5wgaGrmn9Yo/nyvMlq1oBmheVhpHKkZzBlA wztS7jWCmtVtjuN6BQFYSswKzw== X-Google-Smtp-Source: APXvYqxO7YeQBjXOU+eGGVQrPXrPAOjpc1i1oOHM3M8eOjBNMyyAUHPbORgo0jerB6CqEffMajZJ5w== X-Received: by 2002:a81:554b:: with SMTP id j72mr28452897ywb.190.1568282597533; Thu, 12 Sep 2019 03:03:17 -0700 (PDT) Received: from localhost ([2600:380:9c1c:691f:cb4:3daf:a71a:adbc]) by smtp.gmail.com with ESMTPSA id f68sm5773695ywb.96.2019.09.12.03.03.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Sep 2019 03:03:16 -0700 (PDT) Date: Thu, 12 Sep 2019 06:03:15 -0400 From: Josef Bacik To: Anand Jain Cc: Josef Bacik , Eli V , linux-btrfs Subject: Re: [PATCH RFC v2 0/2] readmirror feature Message-ID: <20190912100313.kjdatocumj6bbe7x@MacBook-Pro-91.local> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, Sep 12, 2019 at 06:00:21PM +0800, Anand Jain wrote: > > > > On 12 Sep 2019, at 5:50 PM, Josef Bacik wrote: > > > > On Thu, Sep 12, 2019 at 03:41:42PM +0800, Anand Jain wrote: > >> > >> > >> Thanks for the comments. More below. > >> > >> 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: > >>>>> > >>>>> 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=0. > >>>>>> > >>>>>> 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. > >>>>>> > >>>>>> The new property is stored as an item in the device tree as show below. > >>>>>> (BTRFS_READMIRROR_OBJECTID, BTRFS_PERSISTENT_ITEM_KEY, devid) > >>>>>> > >>>>>> 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 */ > >>>>>> } > >>>>>> > >>>>>> 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 > >>>>>> > >>>>>> 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. > >>>>>> > >>>>>> . 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. > >>>>>> > >>>>>> 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.. > >>>>>> > >>>>>> 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. > >>>>>> > >>>>> > >>>>> This is a lot of infrastructure > >> > >> 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. > >> > >> [1] > >> https://lore.kernel.org/linux-btrfs/be68e6ea-00bc-b750-25e1-9c584b99308f@gmx.com/ > >> > > > > That's a NAK on the prop interface. This is a fs wide policy, not a > > directory/inode policy. > > > >> > >>>>> 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, > >>>>> > >>>>> Josef > >>>> > >>>> 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.) > >>> > >>> 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, > >> > >> I wrote about the readmirror policy framework here[2], > >> I forgot to link it here, sorry about that, my mistake. > >> > >> [2] > >> > >> https://lore.kernel.org/linux-btrfs/1552989624-29577-1-git-send-email-anand.jain@oracle.com/ > >> > >> Readmirror policy is for raid1, raid10 and future N way mirror. > >> Yes for now its only for raid1. > >> > >> Here the idea is to create a framework so that readmirror policy > >> can be configured as needed. And nonrotational can be one such policy. > >> > >> 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. > >> > > > > 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. > > > > 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, > > > > Ok. > Sysfs is fine however we need configuration to be persistent across reboots. > Any idea? > Udev rules. Thanks, Josef