[oi-dev] My FUSE presentation at SCALE last month

[Jean-Pierre André]

Hi Gordon,

Gordon Ross wrote:
> In case anyone would like to have a look, here are the slides from my
> presentation on "FUSE with in-kernel meta-data caching" at SCALE 10x
> last month.
> (Summary: doors based fuse is more efficient by a factor of almost 2:1)
>    http://yalms.org/docs/fuse-scale-2011.pdf
>    

Great, but do not be confused by the implementation bugs
in the fuse kernel module. The cacheing of pages being
written to is wrong : if the application uses a 512 byte
buffer, and the cluster size is 4K, the kernel module sends
512 bytes (0-511)
1024 bytes (0-1023)
1536 bytes (0-1535)
....
4096 bytes (0-4095)
512 bytes (4096-4617)
etc.
So in average each byte is sent twice.

Note : the fuse module looks like it has never been
debugged.

> Here's the doors-based fuse described in the SCALE presentation:
>    https://bitbucket.org/gwr/illumos-fuse2
>    

I do not agree with the need to rebuild the full path
at any stage, at least for a local file system (network
file systems may have different requirements).

At the vnode level, a file is identified by its nodeid
or by a file name in a directory and the nodeid of
the directory. At the file system level, it is just the
same, the full path is not needed anywhere.

Moreover the full path creates complexity when a
file has several paths (hard links) : you have to
make sure a single record in the caches is used
when a file has several names.

Getting rid of the full path may also help managing
ghost files which have been deleted, though kept
open by other processes.

So, why not try to eliminate the "fuse high level" ?

Regards

Jean-Pierre