Re: [ANNOUNCE] ddtree: A git kernel tree for storage servers

[Daniel Phillips <phillips@phunq.net>]

On Wednesday 19 March 2008 13:23, Mike Snitzer wrote:
> >   * Block layer deadlock fixes (Status: production)
> 
> Do you happen to have a pointer to where these block layer deadlock
> fixes are?  Or will you be committing them shortly?

Hi Mike,

OK, this is committed now, but caveat: improved, untested except for
booting.  But what could possibly go wrong? :-/

http://phunq.net/ddtree?p=ddtree/.git;a=blob;f=patches/bio-throttle

The production version is sitting in the code.google.com svn repository
in ddsnap/patches/2.6.23.8.  That one has a known bug that has somehow
escaped being stomped with a new commit, since it only manifests if you
stack one stacking block device on top of another one.  I will post here
when we have an official, torture tested version of the patch.

The patch above is improved from the most recently posted version by
using using the ->bi_max_vecs field for throttle accounting instead of
calling out to a per-driver metric.  This works nicely because the
max_vecs field cannot change during the life of the bio, and it gives
a decent upper bound on the resource consumption of the bio, better
than simply counting bios in flight.  The queue->metric() method is
still in there as a stub, some more cleanup to do there (and further
shrinking of the patch).  It does no harm.

This improvement shrinks the throttled version of struct bio by 4
bytes.

Regards,

Daniel