Yes there is a slight window there, but fsync_dev() serves to flush out the
majority of outstanding I/Os to disk (it waits for I/O completion). All
of these buffers should be on disk, right?
> Even despite of that window we don't even wait the
> requests running just after the lock test to complete, the only lock we
> have is in lvm_map, but we should really track which of those bh are
> been committed successfully to the platter before we can actually copy
> the pv under the lvm from userspace.
As soon as we set LOCK_PE, any new I/Os coming in on the LV device will
be put on the queue, so we don't need to worry about those. We have to
do something like sync_buffers(PV, 1) for the PV that is underneath the
PE being moved, to ensure any buffers that arrived between fsync_dev()
and LOCK_PE are flushed (they are the only buffers that can be in flight).
Is there another problem you are referring to?
AFAICS, there would only be a large window for missed buffers if you
were doing two PE moves at once, and had contention for _pe_lock,
otherwise fsync_dev to LOCK_PE is a very small window, I think.
However, I think we are also protected by the global LVM lock from
doing multiple PE moves at one time.
> If the logic would been sane, your patch would also been ok
> (besides the C breakage of the missing volatile but we abuse gcc this
> way in other parts of the kernel too after all).
Yes, I never thought about GCC optimizing away the two references to the
same var before and after making the check.
> I think the whole pv_move logic needs to be redesigned and rewritten, if
> you could rewrite it and send patches (possibly also against beta7 if
> a new lvm release is not scheduled shortly) that would be more than
Yes, well the correct solution is to do it all in a kernel thread, so
that you don't need to do kernel->user->kernel data copying. I already
discussed this with Joe Thornber (I think) and it was decided to be too
much for now (needs changes to user tools, IOP version, etc). Later.
-- Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto, \ would they cancel out, leaving him still hungry?" http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/