Re: direct_access, pinning and truncation

[Jan Kara <jack@suse.cz>]

On Thu 09-10-14 12:14:02, Zach Brown wrote:
> > > Maybe in the allocator you skip otherwise free blocks if they intersect
> > > with the run time structure (rbtree of extents, presumably) that is
> > > taking the place of reference counts in struct page.  There aren't
> > > *that* many allocator entry points.  I guess you'd need to avoid other
> > > modifications of free space like trimming :/.  It still seems reasonably
> > > doable?
> > 
> > Ah, so on reboot, the on-disk data structures are all correct, and
> > the in-memory data structures went away with the runtime pinning of
> > the memory.  Nice.
> 
> Yeah, that's what I was picturing.  The part I'm most fuzzy on is how to
> get current g_u_p() callers consuming the mappings without full struct
> pages.
  So the direct IO layer could be relatively easily converted to use just
PFNs instead of struct pages. But you'd also have to change block layer
(bios) to work with PFNs instead of struct page and that's going to be
non-trivial IMHO.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR