> On Tuesday 14 August 2007 04:50, Evgeniy Polyakov wrote:
> > On Tue, Aug 14, 2007 at 04:35:43AM -0700, Daniel Phillips
> (
phillips@phunq.net) wrote:
> > > On Tuesday 14 August 2007 04:30, Evgeniy Polyakov wrote:
> > > > > And it will not solve the deadlock problem in general. (Maybe
> > > > > it works for your virtual device, but I wonder...) If the
> > > > > virtual device allocates memory during generic_make_request
> > > > > then the memory needs to be throttled.
> > > >
> > > > Daniel, if device process bio by itself, it has a limit and thus
> > > > it will wait in generic_make_request()
> > >
> > > What will make it wait?
> >
> > gneric_make_request() for given block device.
>
> Not good enough, that only makes one thread wait. Look here:
>
>
http://lkml.org/lkml/2007/8/13/788
>
> An unlimited number of threads can come in, each consuming resources of
> the virtual device, and violating the throttling rules.
>
> The throttling of the virtual device must begin in generic_make_request
> and last to ->endio. You release the throttle of the virtual device at
> the point you remap the bio to an underlying device, which you have
> convinced yourself is ok, but it is not. You seem to miss the fact
> that whatever resources the virtual device has allocated are no longer
> protected by the throttle count *of the virtual device*, or you do not
