[Cluster-devel] [DLM PATCH] DLM: Don't wait for resource library lookups if NOLOOKUP is specified

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
> Can we just use NOQUEUE?  It tells you that there's a lock conflict, which
> tells you to move along and try another if you don't want to contend.  If
> you cache acquired locks and reuse them, then it doesn't matter if the
> master node is remote or local.

The problem with NOQUEUE is that it seems to depend on circumstances.
If each node mounts the file system at a separate time, and as part of that
process, they do a NOQUEUE lock on every rgrp, they all are granted the lock.
With this scheme, they're evenly divided between the nodes.

It doesn't matter anyway, because I'm scrapping the DLM patch in favor of
a scheme like the one you pointed out in GFS1 below. See my other email for
more details.

> If lookups are a problem in general, there is the "nodir" lockspace mode,
> which replaces the resource directory lookup system with a static mapping
> of resources to master nodes.
> 
(snip)
> Back in 2002 I solved what sounds like the same problem in gfs(1).  It
> allowed all nodes to allocate blocks independent of each other, without
> constant locking.  You can see the solution here:
> 
> https://git.fedorahosted.org/cgit/cluster.git/tree/gfs-kernel/src/gfs/rgrp.c?h=RHEL4

Regards,

Bob Peterson
Red Hat File Systems