From: Jan Kara Subject: Re: [PATCH] A request to reserve a "tree id" field on ext[34] inodes Date: Tue, 17 Nov 2009 19:47:15 +0100 Message-ID: <20091117184715.GD1923@atrey.karlin.mff.cuni.cz> References: <4B02AD8B.2030202@openvz.org> <20091117171226.GC1923@atrey.karlin.mff.cuni.cz> <4B02E3AD.3090904@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Andreas Dilger , Theodore Ts'o , Andrew Morton , linux-ext4@vger.kernel.org, Dmitri Monakhov To: Pavel Emelyanov Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:50128 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753143AbZKQSrK (ORCPT ); Tue, 17 Nov 2009 13:47:10 -0500 Content-Disposition: inline In-Reply-To: <4B02E3AD.3090904@openvz.org> 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. Yeah, OK, but it's quite similar :) > > 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. But for implementation, it's kind of important whether there is going to be just one "tree" limitation for each inode, or arbitrary number of them... > > 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 :( Right, that's nasty. OK, but as Andreas suggested, extended attributes are more flexible for this - most notably every fs supporting them would be able to support your tree quota extension. Honza -- Jan Kara SuSE CR Labs