Delayed Extent Tree and Extent Lock Tree

[Allison Henderson <achender@linux.vnet.ibm.com>]

Hi Yongqiang,

I've have been working on an extent lock implementation that uses an 
rbtree to keep track of locked extents, and I think I will probably end 
up with a something similar to the tree that you've already set up for 
delayed extents.  So I wanted to send a note out to see what folks would 
think about the idea of merging the two solutions.

If we did this, the tree would get a little more complex in that it 
would have to keep track of more than just delayed extents. It would 
have to keep track of all extents and the processes that are waiting on 
them.  So I guess it would kind of turn into an extent status tree.  I 
also realize that some folks wanted to see range locks go into /lib as 
general purpose code so that other filesystems or kernel code could use 
it too, but the advantage to this approach would be one less tree for 
ext4 to keep track of.  Any thoughts?

Allison Henderson