[TUHS] FreeBSD behind the times? (was: Favorite unix design principles?)

[Bakul Shah]

On Feb 4, 2021, at 4:33 PM, Larry McVoy <lm at mcvoy.com> wrote:
> 
> Ignoring the page cache and make their own cache has big problems.
> You can mmap() ZFS files and doing so means that when a page is referenced
> it is copied from the ZFS cache to the page cache.  That creates a
> coherency problem, I can write via the mapping and I can write via
> write(2) and now you have two copies of the data that don't match,
> that's pretty much OS no-no #1.

Write(2)ing to a mapped page sounds pretty dodgy. Likely to get you
in trouble in any case. Similarly read(2)ing. And you can keep track of
mapped pages and read/write from them if necessary even if you have
a  separate cache for any compressed pages. I haven’t read zfs code
but this doesn’t seem like a tricky problem.