[Cluster-devel] About locking granularity of gfs2

[Guoqing Jiang]

Hi,

Since gfs2 can "allow parallel allocation from different nodes 
simultaneously
as the locking granularity is one lock per resource group" per section 
3.2 of [1].

Could it possible to make the locking granularity also applies to R/W 
IO? Then,
with the help of "sunit" and "swidth", we basically can lock a stripe, 
so all nodes
can write to different stripes in parallel, so the basic IO unit is one 
stripe.
Since I don't know gfs2 well,  I am wondering it is possible to do it or 
it doesn't
make sense at all for the idea due to some reasons. Any thoughts would be
appreciated, thanks.

I am asking the question because if people want to add the cluster 
support for
md/raid5, then it is better to get the help from filesystem level to 
ensure only one
node can access a stripe at a time, otherwise we have to locking a 
stripe in md
layer which could cause performance issue.

[1] https://www.kernel.org/doc/ols/2007/ols2007v2-pages-253-260.pdf

Regards,
Guoqing