[Pvfs2-developers] Re: pvfs fuse interface

[Murali Vilayannur]

Hi John,

> > Using direct_io avoids the page cache.  Basicaly, direct_io calls
> > back almost immediately into the user space code rather than going
> > through the generic_file_read/write path.  What that also means is
> > that some attrs may not get updated properly if they are getting
> > cached in the kernel.

I did not think that using O_DIRECT causes coherence issues in the VFS caches.
that would be disastrous for databases that rely on O_DIRECT, no?
What attrs don't get updated?

> > O_DIRECT doesn't work in FUSE.  The kernel throws it back on open
> > with an EINVAL.

fuse does not implement the direct_IO or get_xip_page callback in
address_space_operations. Hence EINVAL.

> >
> > Hope I could help.  If you are planning on using the Fuse code that I
> > did, there needs to be some significant testing on your workloads.
> > Also, one major problem with my code is that it doesnt work with
> > multithreaded fuse.

Even if the problem were to be fixed in your code it still wouldn't
work because the PVFS system interfaces are not reentrant.
thanks for the answers!
Murali