On Sat, Aug 09, 2014 at 08:09:51PM -0400, Theodore Ts'o wrote: > On Sun, Aug 10, 2014 at 09:38:32AM +1000, Dave Chinner wrote: > > > > I've seen this sort of thing quite a bit over the past 10 years. > > Most of the time on storage systems measured in the high tens to > > hundreds of TB of storage, which puts it way out of the scope of > > knowledge of most Linux distro and application developers. That's > > most likely why you don't get any other answer to your questions - > > most people can't see how project quotas get used because they've > > never worked in a large, multi-project environment before. > > Sure, but the people who are advocating for project quotas had better > understand how they plan to use them, both so that (a) if they do a > design different from XFS, they can justify why the differences are > necessary, and (b) to justify whether we need it in ext4 to begin > with. > > The "directory hierarchy quota" is easy to understand, it's something > that the Andrew File System had --- down to restriction that you can't > move a file between different AFS volumes, but instead have to copy > and unlink. *nod* - that's the semantics the EXDEV error a cross-project rename in the XFS rename code gives. Looking back at some of the comments in the thread, I suspect that the behaviour this triggers in all userspace utilities isn't clear: separately managed directory hierarchies are designed to appear to userspace as separate filesystems from an accounting and behavioural POV. Note, also, that this means running df on a XFS filesystem with a path inside a directory tree quota heirarchies will report the space used of the direct tree quota, not the overall filesystem... > > If we need a more *complex* solution because people need more than > > just what the simple solution gives them, then that is a topic for > > -fsdevel and probably LSFMM because there's all sorts of semantic > > and interface discussions that are needed and a lot more code that > > needs to be written. i.e. the simple solution can be deployed within > > a couple of kernel releases, a generic solution is more likely a > > coupleof *years* of work to deploy... > > 100% agreed. And I have yet to see a compelling case that even the > simple form of project id's would get a lot of use in the ext4 world. > Which is why I want to know from those who want to add project quotas > in to ext4. How do you plan to use them? What's the use case > scenario? That's fair enough, though I think you'll find that the plain project quota will find many different uses that filesystem developers will have never thought of if it is there. e.g. I came across an embedded NAS device a few years ago implemented with a centralised object stores but had per-export space usage accounting and enforcement by assigning every object associated with a specific exported volume the same project quota.... Fundamentally, project quotas provide a quota mechanism that is independent of both the filesystem heirarchy and the owner credentials of the file. That means it can be used for all sorts of things traditional u/g quotas cannot be used for and directory tree quota is just one of them. As fs developers, we usually talk about directory tree quota because it's the only project quota use case that I've come across that needs kernel/fs help to implement sanely. ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
