Log message:
Install a new sysctl, vfs.lfs.ignore_lazy_sync, which causes LFS to ignore
the "smooth" syncer, as if vfs.sync.*delay = 0, but only for LFS. The
default is "on", i.e., ignore lazy sync.
Reduce the amount of polling/busy-waiting done by lfs_putpages(). To
accomplish this, copied genfs_putpages() and modified it to indicate which
page it was that caused it to return with EDEADLK. fsync()/fdatasync()
should no longer ever fail with EAGAIN, and should not consume huge
quantities of cpu.
Also, try to make dirops less likely to be written as the result of a
VOP_PUTPAGES(), while ensuring that they are written regularly.
