epoch(9) background information?

[Konstantin Belousov]

On Tue, Aug 21, 2018 at 11:44:19PM -0700, Matthew Macy wrote:
> EPOCH_LOCKED is something that one would only want to use in a fairly
> narrow set of circumstances. The only place it's being discussed currently
> is in pmap:
> 
> https://reviews.freebsd.org/D15983
> 
> There it would conceivably replace a global mutex that currently serializes
> all munmap operations.

I have a scetchy design which keeps the current approach of waiting
for delayed invalidation in the pmap_remove_all()/pmap_remove_write(),
simultaneosly eliminating the global_invl_mtx mutex at all.  There was
some discussion about epoch vs. fine-graining of the existing DI code,
relative to the moving the sleep time to pagedaemon threads.

I did not have time to work it out (yet) due to personal issues.