Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains

Christoph Hellwig
2001-02-01T17:05:51Z

On Thu, Feb 01, 2001 at 04:16:15PM +0000, Stephen C. Tweedie wrote:
> Hi,
>
> On Thu, Feb 01, 2001 at 04:09:53PM +0100, Christoph Hellwig wrote:
> > On Thu, Feb 01, 2001 at 08:14:58PM +0530, bsuparna@in.ibm.com wrote:
> > >
> > > That would require the vfs interfaces themselves (address space
> > > readpage/writepage ops) to take kiobufs as arguments, instead of struct
> > > page * . That's not the case right now, is it ?
> >
> > No, and with the current kiobufs it would not make sense, because they
> > are to heavy-weight.
>
> Really? In what way?

We can't allocate a huge kiobuf structure just for requesting one page of
IO. It might get better with VM-level IO clustering though.

>
> > With page,length,offsett iobufs this makes sense
> > and is IMHO the way to go.
>
> What, you mean adding *extra* stuff to the heavyweight kiobuf makes it
> lean enough to do the job??

No. I was speaking abou the light-weight kiobuf Linux & Me discussed on
lkml some time ago (though I'd much more like to call it kiovec analogous
to BSD iovecs).

And a page,offset,length tuple is pretty cheap compared to a current kiobuf.

Christoph

--
Of course it doesn't work. We've performed a software upgrade.