Re: [PATCH] [Request for inclusion] Filesystem in Userspace

Miklos Szeredi
2004-11-25T07:30:52Z

> > There are already "strange" filesystems in the kernel which cannot
> > really get rid of dirty data. I'm thinking of tmpfs and ramfs.
> > Neither of them are prone to deadlock, though both of them are "worse
> > off" than a userspace filesystem, in the sense that they have not even
> > the remotest chance of getting rid of the dirty data.
> >
> > Of course, implementing this is probably not trivial. But I don't see
> > it as a theoretical problem as Linus does.
> >
> > Is there something which I'm missing here?
>
> But they KNOW that they won't be able to get rid of the dirty data. But
> fuse does not.

Why not? I can set bdi->memory_backed to 1 just like ramfs, implement
my own writeback thread, and voila, no deadlock.

Of course I believe, that it's probably easier to tweak the page cache
to teach it that fuse pages _can_ be written back, but not reliably
like a disk filesystem. And there's the small problem of limiting the
number of writable pages allocated to FUSE.

Miklos