Hi Allison,
On 02/01/2012 06:33 AM, Allison Henderson wrote:

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?

We (Taobao) are very interested in this stuff and it should benefit
several of our workload(It is on our todo list for a long time). I guess
Yongqiang's solution is a little bit limited to the only delayed extent
case, and your new solution at least has 2 more benefits:
1. improve the direct i/o read/write
2. speed up the extent search since now we only cache one in
ei_cached_extent.

So please go ahead with your new solution. btw, do you have any timeline
for it? We are glad to provide any help if needed.

Thanks
Tao