From: Pavel Emelyanov Subject: Re: [PATCH] A request to reserve a "tree id" field on ext[34] inodes Date: Tue, 17 Nov 2009 20:55:57 +0300 Message-ID: <4B02E3AD.3090904@openvz.org> References: <4B02AD8B.2030202@openvz.org> <20091117171226.GC1923@atrey.karlin.mff.cuni.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andreas Dilger , "Theodore Ts'o" , Andrew Morton , linux-ext4@vger.kernel.org, Dmitri Monakhov To: Jan Kara Return-path: Received: from mailhub.sw.ru ([195.214.232.25]:37673 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752278AbZKQR5B (ORCPT ); Tue, 17 Nov 2009 12:57:01 -0500 In-Reply-To: <20091117171226.GC1923@atrey.karlin.mff.cuni.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: Jan Kara wrote: > Hi, > >> We have a proposal to implement a 2-level disk quota on ext3 and ext4. >> >> In two words - the aim is to have directories on ext3/4 partitions >> which are limited by its disk usage and the number of inodes. Further >> the plan is to allow configuring uid and gid quotas within them. > If I understand it right, this is something like XFS's project quota, > right? Not exactly. XFS tree quota actually replaces gid one. My proposal is to add the 3rd id. > Note that such thing has implications such as you have to forbid > hardlinks between different "quota trees", otherwise it just won't fly... Yes, I know it. We know other things we'll have to disable, but this is OK to live without them. > Also by 2-level, you mean it won't be possible to nest such subtrees? As I see it - nesting can be done on top of it. I mean - once we have a tree id of an inode and if we say "id A is a sub-id of id B" we're done. As far as containers are concerned - we'll have to map container id to quota tree id, since changing a container id is fast and simple, but it's not so for tree id. That said, this treeid is just a way do distinguish inodes from one sub-tree from the others. > I.e. have a quota on directories a/, b/, a/b, a/c? > >> The main usage of this is containers. When two or more of them are >> located on one disk their roots will be marked with a unique tree id >> and thus the disk consumption of each container will be limited. While >> achieving this goal having an id of what tree an inode belongs to is >> a key requirement. >> >> So first we would like to ask to reserve a place on ext3 and ext4 inodes >> for that ID. > Do you really need to store tree ID on disk? I'd think that it should > be enough to keep some id / pointer in memory and initialize it when we > load inode into memory (from an id / pointer of parent directory). Then > it would be enough to store a fact that some directory is a root of > "quota tree" somewhere - either in extended attributes, as a flag in > the inode, or together with quota data. We can't do it inside ext4_nfs_get_inode unfortunately :( > Honza