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

[Miklos Szeredi]

> > 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
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