> >
> >That means we can maintain the physical size without introducing
> >additional fsync()s in the allocation path. Since we're already
> >writing out the header anyway, the write operation is basically
> >free too.
>
> I don't see how it is free. It's an extra write. The good news is
> that it's very easy to amortize.
We only need to update the header field on disk when we're already
updating the header, so it's not even an extra write operation.
Why would you ever update the header, apart from relocating L1 for
some reason?
To update the L1/L2 tables clean bit. That's what prevents a check in
the normal case where you have a clean shutdown.
Regards,
Anthony Liguori
