On 16 Sep 2000, Trond Myklebust wrote:
>
> Yes. fs/read_write calls the NFS subsystem. The problem then is that
> NFS uses the generic_file_{read,write,mmap}() interfaces. These are
> what enforce use of the page cache.
>
> You could drop these functions, but that would mean designing an
> entire VFS for NFS's use alone. Such a decision would have to be very
> well motivated in order to convince Linus.
Ehh..
I would say that such a decision would be stupid beyond belief, and
impossible to motivate.
NFS certainly doesn't _have_ to use the page cache. However, not using the
page cache would basically in the end be equivalent to
(a) not having coherent mmap's over NFS
(b) probably having much weaker caching
neither of which is really an option at all, I suspect.
You could do caching on your own, but I dare anybody to come up with a
better cache that is able to handle mmap and read/write coherency.
The page granularity issues come from mmap, not from the page cache per
se. ANYTHING that solves the coherency issue is pretty much bound by the
limitations of a page-cache-like thing - they are not limitations of the
implementation, but limitations pretty much inherent to the problem
itself.
Linus
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