Re: Distributed storage.

From: Jens Axboe
Date: Mon Aug 13 2007 - 09:42:21 EST


On Mon, Aug 13 2007, Daniel Phillips wrote:
> On Monday 13 August 2007 02:13, Jens Axboe wrote:
> > On Mon, Aug 13 2007, Daniel Phillips wrote:
> > > On Monday 13 August 2007 00:45, Jens Axboe wrote:
> > > > On Mon, Aug 13 2007, Jens Axboe wrote:
> > > > > > You did not comment on the one about putting the bio
> > > > > > destructor in the ->endio handler, which looks dead simple.
> > > > > > The majority of cases just use the default endio handler and
> > > > > > the default destructor. Of the remaining cases, where a
> > > > > > specialized destructor is needed, typically a specialized
> > > > > > endio handler is too, so combining is free. There are few if
> > > > > > any cases where a new specialized endio handler would need to
> > > > > > be written.
> > > > >
> > > > > We could do that without too much work, I agree.
> > > >
> > > > But that idea fails as well, since reference counts and IO
> > > > completion are two completely seperate entities. So unless end IO
> > > > just happens to be the last user holding a reference to the bio,
> > > > you cannot free it.
> > >
> > > That is not a problem. When bio_put hits zero it calls ->endio
> > > instead of the destructor. The ->endio sees that the count is zero
> > > and destroys the bio.
> >
> > You can't be serious? You'd stall end io completion notification
> > because someone holds a reference to a bio.
>
> Of course not. Nothing I said stops endio from being called in the
> usual way as well. For this to work, endio just needs to know that one
> call means "end" and the other means "destroy", this is trivial.

Sorry Daniel, but your suggestions would do nothing more than uglify the
code and design.

--
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/