zfsonlinux/zfs — pull request #912 by behlendorf (2012-08-29 19:40:08+00:00)
Title: Clear PG_writeback after zil_commit() for sync I/O

When writing via ->writepage() the writeback bit was always cleared
as part of the txg commit callback. However, when the I/O is being
done synchronsously to a slog device we can safely run the callback
immediately after zil_commit().

This will significantly reduce the delay for calls such as fsync()
and msync() which block until the data is safe on disk.

Issue #700
Issue #907