[Linux-cluster] GFS performance tuning

[Bob Peterson]

Hi Ross,

On Tue, 2008-06-10 at 11:55 -0400, Ross Vandegrift wrote:
> On a GFS2 filesystem, I see the following:
> [root at sensor02 ~]# gfs2_tool gettune /rrds
> ...
> statfs_slow = 0
> ...
> 
> Does that indicate that my filesystem is already using this feature?

Yes, GFS2 always uses fast statfs by default.  The code was retrofitted
to GFS (1) by Wendy Cheng (Thanks, Wendy!)

> Do you have any specific reading material you'd suggest on this topic?
> I suspect the interesting bits are related ot how GFS actually uses
> the DLM to lock filesystem metadata.  I've read some of Christine's
> DLM book, but there's not really anything related to GFS therein.

The inner workings of glocks and how GFS and GFS2 use the DLM are
not well documented.  In fact, I don't know of any documents that
exist to explain it.  Steve Whitehouse recently created a "first bash"
glock document and posted it to the cluster-devel mailing list.
You can read it at:

https://www.redhat.com/archives/cluster-devel/2008-June/msg00021.html

The rules for how GFS and GFS2 use the DLM are diverging, so this
document is really a fast-moving target.  What now applies to the
upstream GFS2 does not necessarily apply to the current GFS(1).
Until recently, GFS2 and GFS used the same lock harness, lock_dlm.ko.
However, as time goes on, it is becoming increasingly necessary to
split the lock harness into separate ones for each file system.
This is an ongoing thing right now, upstream at least.  I suspect
that when GFS2 hits RHEL (hopefully for 5.3) there will be two
separate lock harnesses for GFS and GFS2.

> Is the glock trimming patch present in the cluster suite from RH5?

Yes, I glock trimming is available in RHEL5.  I think it was back-
ported to RHEL4 at some level (4.6 maybe?), again by Wendy Cheng.

> The link provided in the Wiki went to a bugzilla bug with no info, and
> URL to people.redhat.com didn't work over https.  I update that, but
> wanted to make sure the Bugzilla link wasn't relevant.

Hm.  Unfortunately, the bugzilla permissions are kind of out of my
control.  I'll see if I can find someone who can change them.

I don't know of a way to make https work on my people page, but http
should work.

I should add that most of the information on my people page is actually
stuff that was created by Wendy Cheng, and she should get the credit.
I had it moved to my account when she left Red Hat so the information
didn't get lost.

Regards,

Bob Peterson
Red Hat Clustering & GFS