Originally this was done in 8a1509e442bc9a075 to forcibly cover cases
where a hole in the directory could be created by extending into
indirect block, since dependency of writing out indirect block is not
tracked. This results in excessive amount of fsyncing the directories,
where all creation of new entry forced fsync before it. This is not needed,
it is enough to fsync when IN_NEEDSYNC is set, and VOP_VPUT_PAIR() provides
the required hook to only perform required syncing.
The series of changes culminating in this commit puts the performance of
metadata-intensive loads back to that before 8a1509e442bc9a075.
Analyzed by: mckusick
Reviewed by: chs, mckusick
Tested by: pho
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
ede40b0675