This reverts commit e92491d95f.
The general idea looked good to me. In particular, it allowed to save
some memory and avoid memory allocation failures when a large buffer
size was requested along with ring and fill policies.
But I didn't take into account that the second, supposedly unused
buffer, was actually used as the scratch buffer. The scratch buffer is
used as a temporary space for DTrace subroutines like copyin, copyinstr,
and alloca.
I think that the change can be fixed by allocating a separate smaller
buffer for the scratch buffer, but that fix would require more work than
I am able to do now. Hence the revert.
Reported by: Domagoj Stolfa
Diagnosed by: Domagoj Stolfa, markj
MFC after: immediately
b9827c007a