From: Greg Freemyer Subject: Re: [PATCH 08/11] ext4: introduce subtree logic Date: Tue, 9 Feb 2010 09:52:37 -0500 Message-ID: <87f94c371002090652w34f91a75m2d832465b113ec98@mail.gmail.com> References: <1265635693-12182-1-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> <87f94c371002090629l6e496b23w8eeb7bbdf3e9b1fe@mail.gmail.com> <87ljf2wjmd.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-f183.google.com ([209.85.223.183]:42835 "EHLO mail-iw0-f183.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754230Ab0BIOwh convert rfc822-to-8bit (ORCPT ); Tue, 9 Feb 2010 09:52:37 -0500 Received: by iwn13 with SMTP id 13so8058229iwn.25 for ; Tue, 09 Feb 2010 06:52:37 -0800 (PST) In-Reply-To: <87ljf2wjmd.fsf@openvz.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Feb 9, 2010 at 9:48 AM, Dmitry Monakhov = wrote: > Greg Freemyer writes: > >> 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 di= rectory >>>>>>> =A0(the subtree root) in T and all of its descendants in T. >>>>>>> >>>>>>> =A0Subtree feature allows to create an isolated (from user poin= t of view) >>>>>>> =A0trees. >>>>>>> >>>>>>> =A0Subtree assumptions: >>>>>>> =A0(1) Each inode has subtree id. This id is persistently store= d 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 i= n other subtree >>>>>>> =A0 =A0 =A0which contradict to isolation criteria. >>>>>>> >>>>>>> =A0This feature is similar to project-id in XFS. One may assign= some id to >>>>>>> =A0a subtree. Each entry from the subtree may be accounted in d= irectory >>>>>>> =A0subtree quota. Will appear in later patches. >>>>>>> >>>>>>> * Disk layout >>>>>>> =A0Subtree id is stored on disk inside xattr usually inside ibo= dy. >>>>>>> =A0Xattr is used only as a data storage, It has not user visiab= le xattr >>>>>>> =A0interface. >>>>>>> >>>>>>> Signed-off-by: Dmitry Monakhov >>>>>> >>>>>> Dmitry, >>>>>> >>>>>> I think the idea of subtrees is useful, but I'm curious about ot= her >>>>>> 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 o= nly be >>>>>> in one subtree at a time. >>>>> Theoretically this is possible, but this dramatically complicate = things >>>>> Just think about this. If inode belongs to different subtrees the= n >>>>> it must have several tree-dquota objects attached to it. This mea= ns >>>>> that quota require great quota redesign. >>>>> Obviously i don't know any use case for this feature. do you know= any? >>>> >>>> Maybe we're talking about different things. =A0I working with the = OHSM >>>> 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 t= o >>>> 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= the >>>> same filesystem because the ohsm subtree geography is not likely t= o be >>>> consistent with the quota subtree geography. >>>> >>>> If we call quota and ohsm services then my desire would be to see = your >>>> subtree patches support orthoganal subtree groups. =A0One group pe= r >>>> 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 t= he >>>> various calls. =A0For a given subtree service group, a given inode= could >>>> 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 = right? >> >> 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] >> { >> =A0 =A0 =A0 =A0__le16 sbe_flags /* entry flags */ >> =A0 =A0 =A0 =A0__le32 sbe_id =A0 =A0/* subtree id */ >> } >> >> (Clearly that won't actually work as is, but you get the idea. =A0Ea= ch >> service group gets its own flags and id.) >> >> Another option would be separate xattr entries for each subtree grou= p. >> >> Regardless, it looks very doable and its just a matter of figuring o= ut >> the best way to support multiple subtree service groups. > Off course i mean that. In fact i'm plan to pack entries in to one > xattr data block because each xattr has significant space overhead. > Sounds great. Does xfs support multiple service groups with its current offering? 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