From: Greg Freemyer Subject: Re: [PATCH 08/11] ext4: introduce subtree logic Date: Tue, 9 Feb 2010 09:29:43 -0500 Message-ID: <87f94c371002090629l6e496b23w8eeb7bbdf3e9b1fe@mail.gmail.com> References: <1265635693-12182-1-git-send-email-dmonakhov@openvz.org> <1265635693-12182-5-git-send-email-dmonakhov@openvz.org> <1265635693-12182-6-git-send-email-dmonakhov@openvz.org> <1265635693-12182-7-git-send-email-dmonakhov@openvz.org> <1265635693-12182-8-git-send-email-dmonakhov@openvz.org> <1265635693-12182-9-git-send-email-dmonakhov@openvz.org> <87f94c371002081554k3e4d6019q332602fea344ccc9@mail.gmail.com> <874olqpvtt.fsf@openvz.org> <87f94c371002090536v2450e67dlb77fa70bfc46cec0@mail.gmail.com> <87sk9awm66.fsf@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-ext4@vger.kernel.org, Jan Kara , OHSM-DEV To: Dmitry Monakhov Return-path: Received: from mail-iw0-f181.google.com ([209.85.223.181]:45426 "EHLO mail-iw0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753361Ab0BIO3p convert rfc822-to-8bit (ORCPT ); Tue, 9 Feb 2010 09:29:45 -0500 Received: by iwn11 with SMTP id 11so178300iwn.17 for ; Tue, 09 Feb 2010 06:29:44 -0800 (PST) In-Reply-To: <87sk9awm66.fsf@openvz.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Feb 9, 2010 at 8:53 AM, Dmitry Monakhov = wrote: > Greg Freemyer writes: > >> On Tue, Feb 9, 2010 at 5:06 AM, Dmitry Monakhov wrote: >>> Greg Freemyer writes: >>> >>>> On Mon, Feb 8, 2010 at 8:28 AM, Dmitry Monakhov wrote: >>>>> * Abstract >>>>> =A0A subtree of a directory tree T is a tree consisting of a dire= ctory >>>>> =A0(the subtree root) in T and all of its descendants in T. >>>>> >>>>> =A0Subtree feature allows to create an isolated (from user point = of view) >>>>> =A0trees. >>>>> >>>>> =A0Subtree assumptions: >>>>> =A0(1) Each inode has subtree id. This id is persistently stored = inside >>>>> =A0 =A0 =A0inode (xattr, usually inside ibody) >>>>> =A0(2) Subtree id is inherent from parent directory >>>>> =A0(3) Inode can not belongs to different subtree >>>>> =A0 =A0 =A0Otherwise changes in one subtree result in changes in = other subtree >>>>> =A0 =A0 =A0which contradict to isolation criteria. >>>>> >>>>> =A0This feature is similar to project-id in XFS. One may assign s= ome id to >>>>> =A0a subtree. Each entry from the subtree may be accounted in dir= ectory >>>>> =A0subtree quota. Will appear in later patches. >>>>> >>>>> * Disk layout >>>>> =A0Subtree id is stored on disk inside xattr usually inside ibody= =2E >>>>> =A0Xattr is used only as a data storage, It has not user visiable= xattr >>>>> =A0interface. >>>>> >>>>> Signed-off-by: Dmitry Monakhov >>>> >>>> Dmitry, >>>> >>>> I think the idea of subtrees is useful, but I'm curious about othe= r >>>> use cases than just quota. >>>> >>>> At first glance you are attempting to create a generic subtree >>>> functionality for ext4, but criteria 3) above says a inode can onl= y be >>>> in one subtree at a time. >>> Theoretically this is possible, but this dramatically complicate th= ings >>> Just think about this. If inode belongs to different subtrees then >>> it must have several tree-dquota objects attached to it. This means >>> that quota require great quota redesign. >>> Obviously i don't know any use case for this feature. do you know a= ny? >> >> Maybe we're talking about different things. =A0I working with the OH= SM >> project >> >> We haven't submitted any patches yet, but for one of our features we >> have something fairly close to your subtree patch. =A0If we were to >> leverage your patch and drop that part of ours we would be in the >> unhappy situation that quota and ohsm could not both be enabled on t= he >> same filesystem because the ohsm subtree geography is not likely to = be >> consistent with the quota subtree geography. >> >> If we call quota and ohsm services then my desire would be to see yo= ur >> subtree patches support orthoganal subtree groups. =A0One group per >> service. >> >> I haven't looked into the actual implementation, but from an API >> perspective it is just a matter of adding a service parameter to the >> various calls. =A0For a given subtree service group, a given inode c= ould >> only be part of one subtree, but a single inode could participate in >> multiple subtree service groups. > Ok now i think i understand what you are talking about. > one subtree <=3D> one service is the main rule i'm standing. > If you wan to support several services, no problem > I can easily extend xattr to support different services > something like this > subtree_entry > { > =A0 =A0 =A0 =A0__le16 sbe_flags /* entry flags */ > =A0 =A0 =A0 =A0__le16 sbe_type =A0/* service type */ > =A0 =A0 =A0 =A0__le32 sbe_id =A0 =A0/* subtree id */ > } Conceptually agreed. But you'd still be limited to one subtree_entry per inode with that rig= ht? Another option would be more like #define EXT4_SUBTREE_MAX_SERVICE_GROUPS 1 #define EXT4_SUBTREE_MAX_SERVICE_GROUP_QUOTA 0 // OHSM would patch the above when its ready to submit subtree_entry[EXT4_SUBTREE_MAX_SERVICE_GROUPS] { __le16 sbe_flags /* entry flags */ __le32 sbe_id /* subtree id */ } (Clearly that won't actually work as is, but you get the idea. Each service group gets its own flags and id.) Another option would be separate xattr entries for each subtree group. Regardless, it looks very doable and its just a matter of figuring out the best way to support multiple subtree service groups. Greg -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html