On Thu, Oct 20, 2011 at 04:39:21PM +0000, David Holland wrote: > > We're talking a few MB of ram here, isn't it ? the kernel can certainly > > allocate this without troubles (other subsystems do). > > The proplib'd and XMLified complete dump for 50,000 users will > probably make a blob of between 10 and 20 MB. (Note: this is an > estimate; I haven't checked the size by trying it. It might be larger. > I'd be surprised if it were much smaller.)
I tested with a few 10s or users; my estimate is about 35MB for 50k users. > > I don't see why it's desirable to manifest such large objects when > it's easily avoidable. We don't agree on "easily". > > > > There are two design truisms for database stuff that apply here: > > > first, you always end up wanting cursors, and second, you always end > > > up wanting bulk get (and not just single get) from those cursors. So > > > it's usually a good idea to anticipate this and design it all in up > > > front. > > > > Maybe ... I know that in the end I want the whole set of data and not > > just a part of it. > > Yes, probably. The cursor API I've floated so far is not general > enough to support much else. Although it could be made more general. > > > But if you believe it's needed this can easily be added to the > > existing quotactl(2) (it would just be a new command). > > Yes, perhaps it could... but why? What's to be gained by using a > baroque proplib encoding of what can otherwise be handled as an array > of simple structs? it's an easily machine-parsable text. That's probably the reason why it's used in other parts of the kernel too. > > I remember asking this question when you first proposed the proplib > interface last spring, and never really got a clear answer. I see it as being the common format used for non-performance-critical kernel/userland communication. It has been adopted by other kernel subsystems, there's prior art there. > > > > > > The reason to wrap the position in a cursor abstraction is to allow > > > > > flexibility about how the position is represented. > > > > > > > > But then the cursor would still be stored in userland ? > > > > > > That's the idea, like reading a file with pread(). > > > > > > I think the kernel should know, or at least be able to know, how many > > > cursors are currently open; but I don't think there's any need to keep > > > the cursor state itself in the kernel. > > > > So you want a quotaopen/quotaclose, with a file descriptor (or something > > similar) ? > > The proposed API already has explicit open and close for cursors; what > I'm saying is that this should be exposed to the kernel. (Open already > has to be, to initialize the cursor position; close should be, so the > filesystem can if necessary know if there are cursors open at any > given time. Otherwise you can get into trouble; see for example nfsd > and readdir.) So you're close to have something like a file descriptor. -- Manuel Bouyer <bou...@antioche.eu.org> NetBSD: 26 ans d'experience feront toujours la difference --