> 2) In uvmhist, half of the string lengths are of the format strings. gcc=20
> will turn strlen("Foo") into a constant (3 in this case) at compile time.=
> =20
> So by storing lengths, our compiler is removing half the calls to=20
> strlen().

Though it is easily fixable, that is not true with current
implementation.

> The uvm history system is designed to handle logging a very busy kernel=20
> subsystem to disk very efficiently.

What do you mean?  I don't think there is such feature (log to disk),
except vmstat > file (and this is not always useful; with the first
item below, it was useful to dump 30000 entries.  it was pain dumping
those on serial console).


...BTW, things I actually needed for uvmhist in the past are:

- knob to stop logging.  this is to prevent the necessary log won't be
  overwritten by others.

- control how timestamp is calcurated; microtime is heavy for some
  situation.

- version of UVMHIST_CALLED() which doesn't call UVMHIST_LOG().
  sometimes it was neccesary to log only on certian condition
  (otherwise the log buffer is filled with `xxx called!').

enami.