[dm-devel] Improve processing efficiency for addition and deletion of multipath devices

[tang.junhui at zte.com.cn]

In these scenarios, multipath processing efficiency is very low:
1) There are many paths in multipath devices,
2) Add/delete devices when iSCSI login/logout or FC link up/down.

Multipath process so slowly that it is not satisfied some applications, 
For example, 
openstack is often timeout in waiting for the creation of multipath 
devices.

The reason of the low processing efficiency I think is that multipath 
process uevent 
message one by one, and each one also produce a new dm 
addition/change/deletion 
uevent message to increased system resource consumption, actually most of 
these uevent 
message have no sense at all.

So, can we find out a way to reduce these uevent messages to promote 
multipath 
processing efficiency? Personally, I think we can merge these uevent 
messages before 
processing. For example, during the 4 iSCSI session login procedures, we 
can wait for a 
moment until the addition uevent messages of 4 paths are all arrived, and 
then we can 
merge these uevent messages to one and deal with it at once. The way to 
deal with 
deletion uevent messages is the same.

How do you think about? Any points of view are welcome.
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