Re: [GIT PULL] fscache rewrite -- please drop for now

[David Wysochanski]

On Mon, Aug 10, 2020 at 11:48 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Steve French <smfrench@xxxxxxxxx> wrote:
>
> > cifs.ko also can set rsize quite small (even 1K for example, although
> > that will be more than 10x slower than the default 4MB so hopefully no
> > one is crazy enough to do that).
>
> You can set rsize < PAGE_SIZE?
>
> > I can't imagine an SMB3 server negotiating an rsize or wsize smaller than
> > 64K in today's world (and typical is 1MB to 8MB) but the user can specify a
> > much smaller rsize on mount.  If 64K is an adequate minimum, we could change
> > the cifs mount option parsing to require a certain minimum rsize if fscache
> > is selected.
>
> I've borrowed the 256K granule size used by various AFS implementations for
> the moment.  A 512-byte xattr can thus hold a bitmap covering 1G of file
> space.
>
>

Is it possible to make the granule size configurable, then reject a
registration if the size is too small or not a power of 2?  Then a
netfs using the API could try to set equal to rsize, and then error
out with a message if the registration was rejected.