Re: CVS commit: syssrc/sys/miscfs/nullfs

[enami tsugutomo <enami%but-b.or.jp@localhost>]

> But we can address this issue, if we want, by arranging for that vnode to
> go on the front of the free list rather than the end.

No, it just makes the lower vnode reclaimed more earlier than it
should be.

> But why?  Why release and grab every time we go on or off the free list,
> when the times it matters (deletion below for instance) are rare, and
> well-defined?

Since, IMHO, keeping reference when it isn't used actually is abuse.

> Think about a case where someone has a web server in a chroot environment,
> and they have read-only null mounted the content into the chroot. Each web
> page is going to result in a path lookup. All of the directories traversed
> in finding a file will come into use (come off of free list), be used for
> a lookup, and then go out of use (go back on the free list). If we don't
> hang onto a ref on the lower vnode, each lookup now has to do a
> reactivate. That seems wasteful to me.

Put vnode back to freelist when it isn't used anymore and reactivating
it when it becomes necessary later is what we do for other
filesystems.  Why we need to handle layerfs specially?

enami.