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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 A42C8C433DF for ; Fri, 29 May 2020 18:54:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C2702074B for ; Fri, 29 May 2020 18:54:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727112AbgE2SyJ (ORCPT ); Fri, 29 May 2020 14:54:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53696 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725795AbgE2SyI (ORCPT ); Fri, 29 May 2020 14:54:08 -0400 Received: from syrinx.knorrie.org (syrinx.knorrie.org [IPv6:2001:888:2177::4d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9FD2DC03E969 for ; Fri, 29 May 2020 11:54:08 -0700 (PDT) Received: from [IPv6:2a02:a213:2b80:f000::12] (unknown [IPv6:2a02:a213:2b80:f000::12]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by syrinx.knorrie.org (Postfix) with ESMTPSA id 2AE0C60927CB4; Fri, 29 May 2020 20:54:07 +0200 (CEST) Subject: Re: [PATCH rfc v3] New ioctl BTRFS_IOC_GET_CHUNK_INFO. To: kreijack@inwind.it, dsterba@suse.cz, linux-btrfs@vger.kernel.org, Josef Bacik References: <20200319203913.3103-1-kreijack@libero.it> <20200319203913.3103-2-kreijack@libero.it> <20200525171430.GX18421@twin.jikos.cz> <5d757a91-503b-64b7-3416-5a26bb03022f@inwind.it> From: Hans van Kranenburg Autocrypt: addr=hans@knorrie.org; keydata= mQINBFo2pooBEADwTBe/lrCa78zuhVkmpvuN+pXPWHkYs0LuAgJrOsOKhxLkYXn6Pn7e3xm+ ySfxwtFmqLUMPWujQYF0r5C6DteypL7XvkPP+FPVlQnDIifyEoKq8JZRPsAFt1S87QThYPC3 mjfluLUKVBP21H3ZFUGjcf+hnJSN9d9MuSQmAvtJiLbRTo5DTZZvO/SuQlmafaEQteaOswme DKRcIYj7+FokaW9n90P8agvPZJn50MCKy1D2QZwvw0g2ZMR8yUdtsX6fHTe7Ym+tHIYM3Tsg 2KKgt17NTxIqyttcAIaVRs4+dnQ23J98iFmVHyT+X2Jou+KpHuULES8562QltmkchA7YxZpT mLMZ6TPit+sIocvxFE5dGiT1FMpjM5mOVCNOP+KOup/N7jobCG15haKWtu9k0kPz+trT3NOn gZXecYzBmasSJro60O4bwBayG9ILHNn+v/ZLg/jv33X2MV7oYXf+ustwjXnYUqVmjZkdI/pt 30lcNUxCANvTF861OgvZUR4WoMNK4krXtodBoEImjmT385LATGFt9HnXd1rQ4QzqyMPBk84j roX5NpOzNZrNJiUxj+aUQZcINtbpmvskGpJX0RsfhOh2fxfQ39ZP/0a2C59gBQuVCH6C5qsY 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1.0 In-Reply-To: <5d757a91-503b-64b7-3416-5a26bb03022f@inwind.it> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 5/29/20 6:23 PM, Goffredo Baroncelli wrote: > On 5/28/20 11:03 PM, Hans van Kranenburg wrote: >> Hi, >> >> On 5/26/20 10:19 PM, Goffredo Baroncelli wrote: >>> On 5/25/20 7:14 PM, David Sterba wrote: >>>> I'll start with the data structures > [...] >>>> >>>> This looks like a copy of btrfs_chunk and stripe, only removing items >>>> not needed for the chunk information. Rather than copying the >>>> unnecessary fileds like dev_uuid in stripe, this should be designed for >>>> data exchange with the usecase in mind. >>> >>> There are two clients for this api: >>> - btrfs fi us >>> - btrfs dev us >>> >>> We can get rid of: >>> - "offset" fields (2x) >>> - "uuid" fields >>> >>> However the "offset" fields can be used to understand where a logical map >>> is on the physical disks. I am thinking about a graphical tool to show this >>> mapping, which doesn't exits yet -). >>> The offset field may be used as key to get further information (like the chunk >>> usage, see below) >>> >>> Regarding the UUID field, I agree it can be removed because it is redundant (there >>> is already the devid) >>> >>> >>>> >>>> The format does not need follow the exact layout that kernel uses, ie. >>>> chunk info with one embedded stripe and then followed by variable length >>>> array of further stripes. This is convenient in one way but not in >>>> another one. Alternatively each chunk can be emitted as a single entry, >>>> duplicating part of the common fields and adding the stripe-specific >>>> ones. This is for consideration. >>>> >>>> I've looked at my old code doing the chunk dump based on the search >>>> ioctl and found that it also allows to read the chunk usage, with one >>>> extra search to the block group item where the usage is stored. As this >>>> is can be slow, it should be optional. Ie. the main ioctl structure >>>> needs flags where this can be requested. >>> >>> This info could be very useful. I think to something like a balance of >>> chunks which are near filled (or near empty). The question is if we >>> should have a different ioctl. >> >> Do you mean that you want to allow to a non root user to run btrfs balance? > No at all. The balance is an expensive operation that IMHO need root > privileges to be started. > >> >> Otherwise, no. IMO convenience functions for quickly retrieving a >> specific subset of data should be created as reusable library functions >> in the calling code, not as a redundant extra IOCTL that has to be >> maintained. > > I think that there is a misunderstood. There is no intention to take the > place of the current balance ioctl. Ok, I'll rephrase. Using it to improve balance is not an argument for adding a new IOCTL, since it has to run as root anyway, and then you can use the SEARCH IOCTL. And as long as there's a few helper functions which do the plumbing, SEARCH isn't that bad at just getting some chunk and block group info. -# python3 >>> import btrfs >>> with btrfs.FileSystem('/') as fs: ... for chunk in fs.chunks(): ... print(fs.block_group(chunk.vaddr)) ... block group vaddr 13631488 length 8388608 flags DATA used 8388608 used_pct 100 block group vaddr 22020096 length 8388608 flags SYSTEM|DUP used 114688 used_pct 1 block group vaddr 30408704 length 1073741824 flags METADATA|DUP used 889061376 used_pct 83 block group vaddr 1104150528 length 1073741824 flags DATA used 1073741824 used_pct 100 block group vaddr 2177892352 length 1073741824 flags DATA used 1073741824 used_pct 100 [...] > The aim of this ioctl is only to get information about the chunk distribution. > Getting the chunk information could help to perform a better balance. > I.e. a balance which start from the chunk more empty the go forward > processing the chunk more filled. An example of this is the existing btrfs-balance-least-used program. > Another case use is to visulize how > the chunk are filled, or how the disks are used.. An example of that is btrfs-heatmap. Hfgl, Hans