When a UFS node is truncated to the zero length, e.g. by explicit truncate(2) call, or by being removed or truncated on open, either new softupdate freeblks structure is allocated to track the freed blocks of the node, or truncation is done syncronously when too many SU dependencies are accumulated. The decision does not take into account the allocated freeblks dependencies, allowing workloads that do huge amount of truncations to exhaust the kernel memory.
When a UFS node is truncated to the zero length, e.g. by explicit
truncate(2) call, or by being removed or truncated on open, either
new softupdate freeblks structure is allocated to track the freed
blocks of the node, or truncation is done syncronously when too many SU
dependencies are accumulated. The decision does not take into account
the allocated freeblks dependencies, allowing workloads that do huge
amount of truncations to exhaust the kernel memory.

Take the number of allocated freeblks into consideration for
softdep_slowdown().

Reported by:	pluknet gmail com
Diagnosed and tested by:	pho
Approved by:	re (rwatson)
MFC after:	1 month

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