Remove all the CSLM#size operation in our memstore because it's an quite time consuming.

Made some performance test for 100% put case in branch-2 before.

We can see that there are many latency peak in p999 latency curve , and the peak time are almost the point time which our region is flushing.

See the hbase20-ssd-put-10000000000-rows-latencys-and-qps

And, I used the add-some-log.patch to log some time consuming when we grab the update.writeLock() to make a memstore snapshot. Tested again, I found those logs in log.txt.

Seems most of the time was consumed when taking memstore snapshot.. Let me dig into this.