Goroutine stack analisys shown some lock contention
while doing massively (100 instances of `docker rm`)
parallel image removal, with many goroutines waiting
for the mountL mutex. Optimize it.
With this commit, the above operation is about 3x
faster, with no noticeable change to container
creation times (tested on aufs and overlay2).
kolyshkin@:
- squashed commits
- added description
- protected CreateRWLayer against name collisions by
temporary assiging nil to ls.mounts[name], and treating
nil as "non-existent" in all the other functions.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
05250a4f00